[Federal Register Volume 61, Number 241 (Friday, December 13, 1996)]
[Proposed Rules]
[Pages 65716-65750]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-30903]


      

[[Page 65715]]

_______________________________________________________________________

Part III





Environmental Protection Agency





_______________________________________________________________________



40 CFR Part 50



National Ambient Air Quality Standards for Ozone; Proposed Rule

  Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / 
Proposed Rules  

[[Page 65716]]



ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 50

[AD-FRL-5659-4]
RIN 2060-AE57


National Ambient Air Quality Standards for Ozone: Proposed 
Decision

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: In accordance with sections 108 and 109 of the Clean Air Act 
(Act), EPA has reviewed the air quality criteria and national ambient 
air quality standards (NAAQS) for ozone (O3) and particulate 
matter (PM). Based on these reviews, the EPA proposes to change the 
standards for both classes of pollutants.
    This document describes EPA's proposed changes with respect to the 
NAAQS for O3. The EPA's proposed actions with respect to PM are 
being proposed elsewhere in today's Federal Register. Nonetheless, EPA 
has concluded that the effects and control of each are in many 
instances linked and will be affected by the other. For this reason, 
EPA intends to review and, as appropriate, modify both standards on a 
similar schedule, with promulgation of revised O3 standards in 
June of 1997, concurrent with promulgation of revised standards for PM. 
Doing so will permit States, localities and industry to address the 
control of these and related pollutants on a more consistent basis.
    Ozone and related pollutants have long been recognized, in both 
clinical and epidemiological research, to affect public health. The 
proposed revised standard would provide protection for children and 
other at-risk populations against a wide range of O3-induced 
health effects, including decreased lung function (primarily in 
children active outdoors), increased respiratory symptoms (particularly 
in highly sensitive individuals), hospital admissions and emergency 
room visits for respiratory causes (among children and adults with pre-
existing respiratory disease such as asthma), inflammation of the lung, 
and possible long-term damage to the lungs.
    With respect to O3, EPA proposes to change the current primary 
standard (last modified in 1979) in several respects:
    1. Since longer exposure periods are of greater concern at lower 
O3 concentrations, attainment of the standard would no longer be 
based upon 1-hour averages, but instead on 8-hour averages. This 
improvement was unanimously recommended by EPA's Clean Air Scientific 
Advisory Committee (CASAC).
    2. As a result of this change in averaging time, the level of the 
standard would be lowered from the present 0.12 parts per million 
(ppm). The EPA solicits comment on alternative levels of 0.09 ppm, 
which generally represents the continuation of the present level of 
protection, and 0.08 ppm, an increased level of protection. Based upon 
its review, EPA is proposing the 0.08 ppm standard to provide increased 
protection for children and asthmatics. The EPA also solicits comment 
on retaining the current primary standard and on an alternative 8-hour 
standard at a level of 0.07 ppm.
    3. In addition, EPA proposes to change the test for attainment 
(i.e., the form) of the new standard. Currently, the test of attainment 
is whether a site exceeds the 1-hour standard on an average of no more 
than once per year, averaged over three years. Given the natural 
variation in hourly O3 levels, this ``one expected exceedance'' 
test can result in relatively unstable attainment/nonattainment 
designations. The CASAC recommended a change to a more stable form; 
consistent with this recommendation, EPA proposes a form based on a 3-
year average of 8-hour O3 concentrations. The EPA solicits comment 
on a range of such concentration-based forms.
    The EPA proposes to replace the current secondary standard with one 
of two alternative standards: one set identical to the proposed new 
primary standard or, alternatively, a new seasonal standard expressed 
as a sum of hourly O3 concentrations greater than or equal to 0.06 
ppm, cumulated over 12 hours per day during the consecutive 3-month 
period of maximum concentrations during the O3 monitoring season, 
set at a level of 25 ppm-hour. Either of the proposed alternative 
secondary standards would provide increased protection against O3-
induced effects, such as agricultural crop loss, damage to forests and 
ecosystems, and visible foliar injury to sensitive species.

DATES: Written comments on this proposed rule must be received by 
February 18, 1997.

ADDRESSES: Submit comments (in duplicate if possible) on the proposed 
rule to: Office of Air and Radiation Docket and Information Center 
(6102) Attn: Docket No. A-95-58, Environmental Protection Agency, 401 M 
St., SW., Washington, DC 20460.
    Public Hearing: The EPA will announce in a separate Federal 
Register document the date, time, and address of the public hearing on 
this proposed rule.

FOR FURTHER INFORMATION CONTACT: Dr. David McKee, MD-15, Air Quality 
Standards and Strategies Division, Office of Air Quality Planning and 
Standards, U.S. Environmental Protection Agency, Research Triangle 
Park, NC 27711, Telephone: (919) 541-5288.

SUPPLEMENTARY INFORMATION:

Docket

    Docket No. A-95-58 incorporates by reference Docket No. A-92-17, 
and the docket established for the air quality criteria document 
(Docket No. ECAO-CD-92-0786). The docket may be inspected between 8:00 
a.m. and 5:30 p.m. on weekdays, and a reasonable fee may be charged for 
copying.

Availability of Related Information

    Certain documents are available from the U.S. Department of 
Commerce, National Technical Information Service, 5285 Port Royal Road, 
Springfield, VA 22161. Available documents include: Air Quality 
Criteria for O3 and Other Photochemical Oxidants (``Criteria 
Document'') (three volumes, EPA/600/P-93-004aF through EPA/600/P-93-
004cF, July 1996, NTIS # PB-96-185574, $169.50 paper copy, $58.00 
microfiche); and the Review of the National Ambient Air Quality 
Standards for O3: Assessment of Scientific and Technical 
Information (``Staff Paper'')(EPA-452/R-96-007, June 1996, NTIS #PB-96-
203435, $67.00 paper copy and $21.50 microfiche). (Add a $3.00 handling 
charge per order.) A limited number of copies of other documents 
generated in connection with this standard review, such as documents 
pertaining to human exposure and health risk assessments, and 
vegetation exposure, risk, and benefits analyses can be obtained from: 
U.S. Environmental Protection Agency Library (MD-35), Research Triangle 
Park, NC 27711, telephone (919) 541-2777. These and other related 
documents are also available for inspection and copying in the EPA 
docket identified above.
    The Staff Paper and human exposure and health risk assessment 
support documents are now available on the Agency's Office of Air 
Quality Planning and Standards (OAQPS) Technology Transfer Network 
(TTN) Bulletin Board System (BBS) in the Clean Air Act Amendments area, 
under Title I, Policy/Guidance Documents. To access the bulletin board, 
a modem and communications software are necessary.

[[Page 65717]]

To dial up, set your communications software to 8 data bits, no parity 
and one stop bit. Dial (919) 541-5742 and follow the on-screen 
instructions to register for access. After registering, proceed to 
choice `` Gateway to TTN Technical Areas'', then choose `` CAAA 
BBS''. From the main menu, choose ``<1> Title I: Attain/Maint of 
NAAQS'', then `` Policy Guidance Documents''. To access these 
documents through the World Wide Web, click on ``TTN BBSWeb'', then 
proceed to the Gateway to TTN Technical areas, as above. If assistance 
is needed in accessing the system, call the help desk at (919) 541-5384 
in Research Triangle Park, NC.

Implementation Activities

    When the proposed revisions to the primary and secondary standards 
are implemented by the States, utility, automobile, petroleum, and 
chemical industries are likely to be affected, as well as other 
manufacturing concerns that emit volatile organic compounds or nitrogen 
oxides. The extent of such effects will depend on implementation 
policies and control strategies adopted by States to assure attainment 
and maintenance of the proposed standards.
    The EPA is developing appropriate policies and control strategies 
to assist States in the implementation of the proposed revisions to 
both the primary and secondary O3 NAAQS. The resulting 
implementation strategies will then be published for public comment in 
the future.

Table of Contents

    The following topics are discussed in today's preamble:

I. Background
    A. Legislative Requirements
    B. Related Control Requirements
    C. Review of Air Quality Criteria and Standards for O3
II. Rationale for Proposed Decision on the Primary Standard
    A. Health Effects Information
    1. Effects of Short-term and Prolonged O3 Exposures
    2. Potential Effects of Long-term O3 Exposures
    3. Adversity of Effects for Individuals
    B. Human Exposure and Risk Assessments
    C. Conclusions on the Elements of the Primary Standard
    1. Averaging Time
    2. Level
    3. Form
    D. Proposed Decision on the Primary Standard
III. Communication of Public Health Information
IV. Rationale for Proposed Decision on the Secondary Standard
    A. Effects on Vegetation
    B. Biologically Relevant Exposure Indices
    C. Vegetation Exposure and Risk Analyses
    D. Conclusions on the Elements of the Secondary Standard
    1. Averaging Time
    2. Form
    3. Level
    E. Proposed Decision on the Secondary Standard
V. Revisions to Appendix H--Interpretation of the NAAQS for Ozone
    A. Data Completeness
    B. Data Handling and Rounding Conventions
VI. Technical Changes to Appendices D and E
VII. Implementation Program
VIII. Regulatory and Environmental Impact Analyses References

I. Background

A. Legislative Requirements

    Two sections of the Act govern the establishment, review, and 
revision of NAAQS. Section 108 (42 U.S.C. 7408) directs the 
Administrator to identify pollutants which ``may reasonably be 
anticipated to endanger public health and welfare'' and to issue air 
quality criteria for them. These air quality criteria are to 
``accurately reflect the latest scientific knowledge useful in 
indicating the kind and extent of all identifiable effects on public 
health or welfare which may be expected from the presence of [a] 
pollutant in the ambient air * * *.''
    Section 109 (42 U.S.C. 7409) directs the Administrator to propose 
and promulgate ``primary'' and ``secondary'' NAAQS for pollutants 
identified under section 108. Section 109(b)(1) defines a primary 
standard as one ``the attainment and maintenance of which, in the 
judgment of the Administrator, based on the criteria and allowing an 
adequate margin of safety, [are] requisite to protect the public 
health.'' The margin of safety requirement was intended to address 
uncertainties associated with inconclusive scientific and technical 
information available at the time of standard setting, as well as to 
provide a reasonable degree of protection against hazards that research 
has not yet identified. Both kinds of uncertainties are components of 
the risk associated with pollution at levels below those at which human 
health effects can be said to occur with reasonable scientific 
certainty. Thus, by selecting primary standards that provide an 
adequate margin of safety, the Administrator is seeking not only to 
prevent pollution levels that have been demonstrated to be harmful but 
also to prevent lower pollutant levels that she finds may pose an 
unacceptable risk of harm, even if the risk is not precisely identified 
as to nature or degree. The Act does not require the Administrator to 
establish a primary NAAQS at a zero-risk level but rather at a level 
that reduces risk sufficiently so as to protect public health with an 
adequate margin of safety.
    A secondary standard, as defined in section 109(b)(2), must 
``specify a level of air quality the attainment and maintenance of 
which, in the judgment of the Administrator, based on [the] criteria, 
[are] requisite to protect the public welfare from any known or 
anticipated adverse effects associated with the presence of [the] 
pollutant in the ambient air.'' Welfare effects as defined in section 
302(h) (42 U.S.C. 7602(h)) include, but are not limited to, ``effects 
on soils, water, crops, vegetation, manmade materials, animals, 
wildlife, weather, visibility and climate, damage to and deterioration 
of property, and hazards to transportation, as well as effects on 
economic values and on personal comfort and well-being.''
    Section 109(d)(1) of the Act requires periodic review and, if 
appropriate, revision of existing air quality criteria and NAAQS. 
Section 109(d)(2) requires appointment of an independent scientific 
review committee to review criteria and standards and recommend new 
standards or revisions of existing criteria and standards, as 
appropriate. The committee established under section 109(d)(2) is known 
as the Clean Air Scientific Advisory Committee (CASAC), a standing 
committee of EPA's Science Advisory Board.

B. Related Control Requirements

    States are primarily responsible for ensuring attainment and 
maintenance of ambient air quality standards once EPA has established 
them. Under section 110 of the Act (42 U.S.C. 7410) and related 
provisions, States are to submit, for EPA approval, State 
implementation plans (SIP's) that provide for the attainment and 
maintenance of such standards through control programs directed to 
sources of the pollutants involved. The States, in conjunction with 
EPA, also administer the prevention of significant deterioration 
program (42 U.S.C. 7470-7479) for these pollutants. In addition, 
Federal programs provide for nationwide reductions in emissions of 
these and other air pollutants through the Federal Motor Vehicle 
Control Program under title II of the Act (42 U.S.C. 7521-7574), which 
involves controls for automobile, truck, bus, motorcycle, and aircraft 
emissions; the new source performance standards under section 111 (42 
U.S.C. 7411); and the national emission standards for hazardous air 
pollutants under section 112 (42 U.S.C. 7412).

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C. Review of Air Quality Criteria and Standards for O3

    The last review of O3 air quality criteria and standards was 
completed in March 1993 with notice of a final decision not to revise 
the existing primary and secondary standards (58 FR 13008). The 
existing primary and secondary standards are each set at a level of 
0.12 ppm, with a 1-hour averaging time and a 1-expected-exceedance 
form, such that the standards are attained when the expected number of 
days per calendar year with maximum hourly average concentrations above 
0.12 ppm is equal to or less than 1, averaged over 3 years (as 
determined by 40 CFR Part 50, Appendix H).1
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    \1\ A more complete history of the O3 NAAQS is presented in 
section II.B of the Office of Air Quality Planning and Standards 
Staff Paper, Review of National Ambient Air Quality Standards for 
O3: Assessment of Scientific and Technical Information (U.S. 
EPA, 1996b).
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    The EPA initiated this current review in August 1992 with the 
development of a revised Air Quality Criteria Document for O3 and 
Other Photochemical Oxidants (henceforth the ``Criteria Document''). 
Several workshops were held by EPA's National Center for Environmental 
Assessment (NCEA) to discuss health and welfare effects information 
during the summer and fall of 1993. An external review draft of the 
Criteria Document made available to the public and to the CASAC in the 
spring of 1994 was reviewed at a public CASAC meeting held on July 30-
31, 1994. Based on comments made at the meeting, NCEA staff prepared a 
second external review draft, which was reviewed at a public CASAC 
meeting on March 20-21, 1995. At the same meeting, the CASAC also 
reviewed draft portions of a staff paper prepared by the Office of Air 
Quality Planning and Standards (OAQPS), Review of National Ambient Air 
Quality Standards for Ozone: Assessment of Scientific and Technical 
Information (henceforth, the ``Staff Paper''), focusing on health 
effects and the primary NAAQS. Taking into account CASAC and public 
comments, staff revised both documents and made new drafts available 
for public and CASAC review during the summer of 1995. The OAQPS staff 
also prepared and made available draft portions of the Staff Paper 
focusing on welfare effects and the secondary standard.
    A public CASAC meeting was held on September 19-20, 1995, at which 
time CASAC came to closure in its review of the draft Criteria Document 
and the primary standard sections of the draft Staff Paper. In a 
November 28, 1995 letter from the CASAC chair to the Administrator, 
CASAC advised that the final draft Criteria Document ``provides an 
adequate review of the available scientific data and relevant studies 
of O3 and related photochemical oxidants'' (Wolff, 1995a). 
Further, in a November 30, 1995 letter, CASAC advised the Administrator 
that the primary standard portion of the draft Staff Paper ``provides 
an adequate scientific basis for making regulatory decisions concerning 
a primary O3 standard'' (Wolff, 1995b). The final Criteria 
Document (U.S. EPA, 1996a) reflects CASAC and public comments received 
at and subsequent to the September 1995 CASAC meeting.
    Based on comments on the Staff Paper from the September 1995 CASAC 
meeting, revisions were made to the secondary standard sections of the 
Staff Paper, which were reviewed at a public CASAC meeting held on 
March 21, 1996. At that meeting and in a subsequent letter to the 
Administrator, CASAC concluded that the secondary standard sections of 
the draft Staff Paper ``provide an appropriate scientific basis for 
making regulatory decisions concerning a secondary O3 standard'' 
(Wolff, 1996).
    The focus of this current review of the air quality criteria and 
standards for O3 and related photochemical oxidants is on public 
health and welfare effects associated with exposure to ambient levels 
of tropospheric O3. Tropospheric O3 is chemically identical 
to stratospheric O3, which is produced miles above the earth's 
surface and provides a protective shield from excess ultraviolet 
radiation. In contrast, tropospheric O3 at sufficient 
concentrations has been associated with harmful effects due to its 
oxidative properties and its presence in the air that people and plants 
take up during respiratory processes. Ozone is not emitted directly 
from mobile or stationary sources but, like other photochemical 
oxidants, commonly exists in the ambient air as an atmospheric 
transformation product. Ozone formation is the result of chemical 
reactions of volatile organic compounds (VOC), nitrogen oxides 
(NOX), and oxygen in the presence of sunlight and generally at 
elevated temperatures. A detailed discussion of atmospheric formation, 
ambient concentrations, and health and welfare effects associated with 
exposure to O3 can be found in the final Criteria Document (U.S. 
EPA, 1996a) and in the final Staff Paper (U.S. EPA, 1996b).
    This review of the scientific criteria for O3 has occurred 
simultaneously with the review of the criteria for particulate matter 
(PM). These criteria reviews, as well as related implementation 
strategy activities to date, have brought out important linkages 
between PM and O3. A number of community epidemiological studies 
have found similar health effects to be associated with exposure to PM 
and O3, including, for example, aggravation of respiratory disease 
(e.g., asthma), increased respiratory symptoms, and increased hospital 
admissions and emergency room visits for respiratory causes. Laboratory 
studies have suggested potential interactions between O3 and 
various constituents of PM. Other key similarities relating to exposure 
patterns and implementation strategies exist between PM, specifically 
fine particles, and O3. These similarities include: (1) 
Atmospheric residence times of several days, leading to large urban and 
regional-scale transport of the pollutants; (2) similar gaseous 
precursors, including NOX and VOC, which contribute to the 
formation of both O3 and fine particles in the atmosphere; (3) 
similar combustion-related source categories, such as coal and oil-
fired power generation and industrial boilers and mobile sources, which 
emit particles directly as well as gaseous precursors of particles 
(e.g., sulfur oxides (SOX), NOX, VOC) and O3 (e.g., 
NOX, VOC); and (4) similar atmospheric chemistry driven by the 
same chemical reactions and intermediate chemical species that form 
both high fine particle and O3 levels. High fine particle levels 
are also associated with significant impairment of visibility on a 
regional scale.
    These similarities provide opportunities for optimizing technical 
analysis tools (i.e., monitoring networks, emission inventories, air 
quality models) and integrated emission reduction strategies to yield 
important co-benefits across various air quality management programs. 
These co-benefits could result in a net reduction of the regulatory 
burden on some source category sectors that would otherwise be impacted 
by separate O3, PM, and visibility protection control strategies.
    In recognition of the multiple linkages and similarities in effects 
and the potential benefits of integrating the Agency's approaches to 
providing for appropriate protection of public health and welfare from 
exposure to PM and O3, EPA is conducting the reviews of the NAAQS 
for both pollutants on the same schedule. Accordingly, today's Federal 
Register contains a separate notice announcing proposed revisions to 
the PM NAAQS. Linking the PM and O3 review schedules provides an 
important

[[Page 65719]]

opportunity for more effective and efficient air quality management--
both in terms of communicating a more complete description of the 
health and welfare effects associated with the major components of 
urban and regional air pollution, and by helping the States and local 
areas to plan jointly to address both PM and O3 air pollution at 
the same time with one process, and to work jointly with industry to 
address common sources of air pollution. The EPA believes this 
integrated approach will lead to more effective and efficient 
protection of public health and the environment.

II. Rationale for Proposed Decision on the Primary Standard

    This notice presents the Administrator's proposed decision to 
replace the existing 1-hour O3 primary NAAQS with a new 8-hour 
standard, based on a thorough review, in the Criteria Document, of the 
latest scientific information on human health effects associated with 
exposure to ambient levels of O3, including evaluation of key 
studies published through 1995. This decision also takes into account 
and is consistent with: (1) Staff assessments of the most policy-
relevant information in the Criteria Document and staff analyses of 
human exposure and risk, presented in the Staff Paper, upon which staff 
recommendations for a new O3 primary standard are based; (2) CASAC 
advice and recommendations, as reflected in discussion of drafts of the 
Criteria Document and Staff Paper at public meetings, in separate 
written comments, and in CASAC's letters to the Administrator; and (3) 
public comments received during the development of these documents, 
either in connection with CASAC meetings or separately.
    The rationale for the proposed revisions of the O3 primary 
NAAQS includes consideration of: (1) Health effects information to 
inform judgments as to the likelihood that exposures to ambient O3 
result in adverse health effects for exposed individuals; (2) insights 
gained from human exposure and risk assessments to provide a broader 
perspective for judgments about protecting public health from the risks 
associated with O3 exposure; (3) specific conclusions with regard 
to the elements of a standard (i.e., averaging time, level, and form) 
that, taken together, would be appropriate to protect public health 
with an adequate margin of safety; and (4) alternative views of the 
significance of the effects and factors to be considered in policy 
judgments about the appropriate level of the standard.

A. Health Effects Information 

    The following summary of human health effects associated with 
exposure to ambient levels of O3 is based on integrative 
information from human clinical, epidemiological, and animal 
toxicological studies, as presented in the Criteria Document and Staff 
Paper. Based on this information, an array of health effects has been 
attributed to short-term (1 to 3 hours), prolonged (6 to 8 hours), and 
long-term (months to years) exposures to O3. Acute health effects 
2 induced by short-term exposures to O3, generally while 
individuals were engaged in heavy exertion, include transient pulmonary 
function responses, transient respiratory symptoms, and effects on 
exercise performance. The current O3 primary NAAQS is generally 
based on these acute effects associated with heavy exercise and short-
term exposures. Other health effects associated with short-term or 
prolonged O3 exposures include increased airway responsiveness, 
susceptibility to respiratory infection, increased hospital admissions 
and emergency room visits, and transient pulmonary inflammation.
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    \2\ ``Acute health'' effects of O3 are defined as those 
effects induced by short-term and prolonged exposures to O3. 
Examples of these effects are functional, symptomatic, biochemical, 
and physiologic changes.
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    Since the last review of the air quality criteria for O3 was 
completed, available information has increased substantially on effects 
associated with prolonged and long-term exposures. Based on this new 
information, similar acute health effects have been observed following 
prolonged exposures at concentrations of O3 as low as 0.08 ppm and 
at moderate levels of exertion.\2\ Although chronic effects 3 such 
as structural damage to pulmonary tissue and carcinogenicity have been 
investigated in a substantial number of laboratory animal studies, 
these effects have not been adequately established in human studies to 
draw any conclusions at this time.
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    \3\ ``Chronic health'' effects of O3 are defined as those 
effects induced by long-term exposures to O3. Examples of these 
effects are structural damage to lung tissue and accelerated decline 
in baseline lung function.
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    This array of effects is briefly summarized below for short-term 
and prolonged O3 exposures, and for long-term O3 exposures. 
Further, judgments are presented with respect to when these 
physiological effects become so significant that they should be 
regarded as adverse to the health of individuals experiencing the 
effects.
1. Effects of Short-term and Prolonged O3 Exposures

a. Pulmonary Function Responses

    Transient reductions in pulmonary function have been observed in 
healthy individuals and those with impaired respiratory symptoms (e.g., 
asthmatic individuals) as a result of both short-term and prolonged 
exposures to O3. The strongest and most quantifiable exposure-
response information on such pulmonary function responses to O3 
has come from controlled human exposure studies. The evidence from such 
studies clearly shows that reductions in lung function are enhanced by 
increased levels of activity involving exertion, typically reported as 
``exercise'' in clinical studies, and by increased O3 
concentrations. Pulmonary function decrements generally tend to return 
to baseline levels shortly after short-term exposure, and effects are 
typically attenuated upon repeated short-term exposures over several 
days.
    As discussed in section V.C.1 of the Staff Paper, numerous 
experimental studies of exercising adults have demonstrated decrements 
in lung function both for exposures of 1-3 hours at 0.12 ppm 
O3 and for exposures of 6.6 hours at 0.08 ppm O3. 
These studies provide conclusive evidence that O3 levels commonly 
monitored in the ambient air induce lung function decrements in 
exercising adults. The extent of lung function decrements varies 
considerably among individuals. Further, numerous summer camp studies 
provide an extensive and reliable database on lung function responses 
to ambient O3 and other pollutants in children and adolescents 
living in the Northeastern U.S., southern California, and Southern 
Canada. Lung function changes reported at ambient O3 
concentrations in these studies are comparable to those reported in 
children and adults exposed under controlled experimental conditions, 
although direct comparisons are difficult to make because of 
differences in experimental design and analytical approach.

b. Respiratory Symptoms and Effects on Exercise Performance

    As discussed in section V.C.2 of the Staff Paper, various transient 
human respiratory symptoms, including cough, throat irritation, chest 
pain on deep inspiration, nausea, and shortness of breath, have been 
induced by O3 exposures of both healthy individuals and those with 
impaired respiratory systems. Increasing O3 exposure durations and 
levels have been shown to elicit increasingly more severe

[[Page 65720]]

symptoms that persist for longer periods in increasingly larger numbers 
of individuals. Symptomatic and pulmonary function responses follow a 
similar time course during an acute exposure and the subsequent 
recovery, as well as over the course of several days during repeated 
exposures. As with pulmonary function responses, the severity of 
symptomatic responses varies considerably among subjects. For some 
outdoor workers or active people who are highly responsive to ambient 
O3, respiratory symptoms may cause reduced productivity or may 
curb the ability or desire to engage in normal activities. Furthermore, 
O3-induced interference with exercise performance, either by 
reducing maximal sustainable levels of activity or reducing the 
duration of activity that can be tolerated at a particular work level, 
is likely related to such symptomatic responses.

c. Increased Airway Responsiveness

    Increased airway responsiveness is an indication that the airways 
are predisposed to bronchoconstriction which can be induced by a wide 
variety of external stimuli (e.g., pollens, dust, cold air, sulfur 
dioxide (SO2), etc.). A high level of bronchial responsiveness is 
characteristic of asthma. Ozone exposure causes increased 
responsiveness of the pulmonary airways to subsequent challenge with 
bronchoconstrictor drugs such as histamine or methacholine. Changes in 
airway responsiveness tend to resolve somewhat more slowly than 
pulmonary function changes, typically disappearing after 24 hours, and 
appear to be less likely to attenuate with repeated exposure.
    As a result of increased airway responsiveness induced by O3 
exposure, human airways may be more susceptible to a variety of 
stimuli, including antigens, chemicals, and particles. For example, as 
cited in section V.C.3 of the Staff Paper, healthy subjects after being 
exposed to O3 concentrations as low as 0.20 ppm for 1 hour and 
0.08 ppm for 6.6 hours have experienced small increases in nonspecific 
bronchial responsiveness, which usually resolve within 24 hours. 
Asthmatic subjects typically have increased airway responsiveness at 
baseline. Whereas the differences in baseline nonspecific bronchial 
responsiveness between healthy individuals and sensitive asthmatics may 
be as much as 100-fold, changes induced by O3 exposure are usually 
only 2- to 4-fold. With regard to O3-induced increases in airway 
responsiveness (e.g., to specific inhaled antigens, cold air, and 
SO2) ongoing studies will need to be completed and evaluated 
before conclusions can be drawn. Because enhanced response to antigens 
in asthmatics could lead to increased morbidity (i.e., medical 
treatment, emergency room visits, hospital admissions) or to more 
persistent alterations in airway responsiveness, these health endpoints 
raise concern for public health, particularly for individuals with 
impaired respiratory systems.

d. Increased Susceptibility to Respiratory Infection

    When functioning normally, the human respiratory tract, like that 
of other mammals, has numerous closely integrated defense mechanisms 
that provide protection from the adverse effects of a wide variety of 
inhaled particles and microbes. To the extent that these defense 
mechanisms can be broken down or impaired by the inhalation of O3, 
as discussed in section V.C.4 of the Staff Paper, O3 exposures can 
result in increased susceptibility to respiratory infection and related 
respiratory dysfunction. Evidence of such effects has come primarily 
from a very large number of laboratory animal studies with generally 
consistent results. One of the few studies of moderately exercising 
human subjects exposed to 0.08 ppm O3 for 6.6 hours reported 
decrements in alveolar macrophage function, the first line of defense 
against inhaled microorganisms and particles in the lower airways and 
air sacs.
    No single experimental human study or group of animal studies 
conclusively demonstrates that human susceptibility to respiratory 
infection is increased by exposure to O3. However, taken as a 
whole, the data suggest that acute O3 exposures can impair the 
host defense capability of both humans and animals, possibly by 
depressing alveolar macrophage function and perhaps also by decreasing 
mucociliary clearance of inhaled particles and microorganisms. This 
suggests that humans exposed to O3 may be predisposed to bacterial 
infections in the lower respiratory tract. The seriousness of such 
infections may depend on how quickly bacteria develop virulence factors 
and how rapidly mechanisms are mobilized to compensate for depressed 
alveolar macrophage function.

e. Hospital Admissions and Emergency Room Visits

    Increased summertime hospital admissions and emergency room visits 
for respiratory causes have been associated with ambient exposures to 
O3 and other environmental factors. As cited in section V.C.5 of 
the Staff Paper, numerous studies conducted in various locations in the 
Eastern United States (U.S.) and Canada consistently have shown a 
relationship between ambient O3 levels and increased incidence of 
emergency room visits and hospital admissions for respiratory causes, 
even after controlling for modifying factors, as well as when 
considering only concentrations <0.12 ppm O3. Such associations 
between elevated ambient O3 during summer months and increased 
hospital admissions have a plausible biological basis in the human and 
animal evidence of functional, symptomatic, and physiologic effects 
discussed above and in the increased susceptibility to respiratory 
infections observed in laboratory animals.
    Individuals with preexisting respiratory disease (e.g., asthma, 
chronic obstructive pulmonary disease) may generally be at increased 
risk of such effects, and some individuals with respiratory disease may 
have an inherently greater sensitivity to O3. On the other hand, 
individuals with more severe respiratory disease are less likely to 
engage in the level of exertion associated with provoking responses to 
O3 exposures in healthy humans. On balance, it is reasonable to 
conclude that evidence of O3-induced increased airway resistance, 
nonspecific bronchial responsiveness, susceptibility to respiratory 
infection, increased airway permeability, airway inflammation, and 
incidence of asthma attacks suggests that ambient O3 exposure 
could be a cause of increased hospital admissions, particularly for 
asthmatics.

f. Pulmonary Inflammation

    Respiratory inflammation can be considered to be a host response to 
injury and indicators of inflammation as evidence that respiratory cell 
damage has occurred. Inflammation induced by exposure of humans to 
O3 may have several potential outcomes: (1) Inflammation induced 
by a single exposure (or even several exposures over the course of a 
season) could resolve entirely; (2) repeated acute inflammation could 
develop into a chronic inflammatory state; (3) continued inflammation 
could alter the structure and function of other pulmonary tissue, 
leading to disease processes such as fibrosis; (4) inflammation could 
interfere with the body's host defense response to particles and 
inhaled microorganisms, particularly in potentially vulnerable 
populations such as children and older individuals; and (5) 
inflammation could amplify the lung's response to other agents such as 
allergens or toxins. For humans, only the first of these potential

[[Page 65721]]

outcomes has been demonstrated in the laboratory. However, this is 
expected because regulations concerning human experimental studies 
require that long-term damage be avoided. Hence, study protocols only 
involved brief exposures.
    Exposures of laboratory animals to O3 for periods 8 
hours have been shown to result in cell damage, inflammation, and 
increased leakage of proteins from blood into the air spaces of the 
respiratory tract. In general, higher O3 concentrations are 
required to elicit a response equivalent to that of humans. This may 
partly result from study design differences, in which humans were 
exposed while exercising, whereas most animal studies were done at 
rest, resulting in differences in effective ventilation rates. 
Laboratory animals studies done at night, during the animals' active 
period, or in which ventilation rates were increased with coexposure to 
carbon dioxide (CO2) tend to support this view. The extent and 
course of inflammation and its constitutive elements has been evaluated 
by using bronchoalveolar lavage (BAL) to sample cells and fluid from 
the lung and lower airways of humans exposed to O3. Several such 
studies cited in section V.C.7 of the Staff Paper have shown that 
exercising humans exposed (1 to 4 hours) to 0.2 to 0.6 ppm O3 had 
O3-induced markers of inflammation and cell damage. The lowest 
concentration of prolonged O3 exposure tested in humans, 0.08 ppm 
for 6.6 hours with moderate exercise, also induced small but 
statistically significant increases in these endpoints.
    Thus, it is reasonable to conclude that repeated acute inflammatory 
response and cellular damage discussed above is potentially a matter of 
public health concern; however, it is also recognized that most, if not 
all, of these effects begin to resolve in most individuals within 24 
hours if the exposure to O3 is not repeated. Of possibly greater 
public health concern is the potential for chronic respiratory damage 
which could be the result of repeated O3 exposures occurring over 
a season or a lifetime. Evidence for these chronic effects is discussed 
below.
2. Potential Effects of Long-term O3 Exposures
    Epidemiologic studies that have investigated potential associations 
between long-term O3 exposures and chronic respiratory effects in 
humans thus far have provided only suggestive evidence of such a 
relationship. Most studies investigating this association have been 
cross-sectional in design and have been compromised by incomplete 
control of confounding variables and inadequate exposure information. 
Other studies have attempted to follow variably exposed groups 
prospectively. As cited in Section V.C.8 of the Staff Paper, studies 
conducted in southern California and Canada have compared lung function 
changes over several years between populations living in communities 
with high and low ambient O3 levels. The findings suggest small, 
but consistent, decrements in lung function among inhabitants of the 
more highly polluted communities; however, associations between O3 
and other copollutants and problems with study population loss have 
reduced the level of confidence in these conclusions.
    In a large number of animal toxicology studies, ``lesions'' 4 
in the centriacinar regions of the lung (i.e., the portion of the lung 
where the region that conducts air and the region that exchanges gas 
are joined) are well established as one of the hallmarks of O3 
toxicity. Studies have been conducted using rats, mice, and primates. 
In one study in which rats were exposed to an urban pattern of O3 
exposure, changes indicative of cell and tissue damage were reported, 
although post-exposure damage was mainly reversible. A similar study of 
identically exposed groups of rats found: (1) Increases in expiratory 
resistance suggesting central airway narrowing after 78 weeks of 
exposure, (2) reduced tidal volumes at all evaluation times during the 
exposure, and (3) generally reduced breathing frequency, although no 
single evaluation time was statistically significant. Another related 
study with a similar protocol reported reduced lung volume, which is 
consistent with a ``stiffer'' lung (i.e., restrictive lung disease). A 
recent multicenter chronic study illustrates some of the complex 
interrelationships among the structural, functional, and biochemical 
effects. The three types of health endpoints mentioned above were 
evaluated in a collaborative project using rats exposed for 20 months. 
Lung biochemistry and structure were affected at 0.5 ppm and 1.00 ppm 
O3, but not at 0.12 ppm O3, although no effects on pulmonary 
function were observed at any exposure level.
---------------------------------------------------------------------------

    \4\ Differing views have been expressed by CASAC panel members 
regarding the use of the term ``lesion'' to describe the O3-
induced morphological (i.e., structural) abnormalities observed in 
toxicological studies. Section V.C.8 of the Staff Paper describes 
and discusses these degenerative changes in more detail.
---------------------------------------------------------------------------

    In summary, the collective data on long-term exposure to O3 
garnered in studies of laboratory animals and human populations have 
many ambiguities. It is clear from toxicology data that the 
distribution of O3 ``lesions'' is roughly similar across species 
(including monkeys, rats, mice) with responses that are concentration 
dependent (and perhaps time or exposure-pattern dependent). Under 
certain conditions, some of these structural changes may become 
irreversible. It is unclear, however, whether ambient exposure 
scenarios encountered by humans result in similar ``lesions'' or 
whether there are resultant functional or impaired health outcomes in 
humans chronically exposed to O3. The epidemiologic lung function 
studies generally parallel those of the animal studies, but these 
studies lack good information on individual O3 exposure history 
and are frequently confounded by personal or copollutant variables. 
Thus, the Administrator recognizes that there is a lack of a clear 
understanding of the significance of repeated, long-term inflammatory 
responses, and that there is a need for continued research in this 
important area. Nevertheless, the currently available information 
provides at least a biologically plausible basis for considering the 
possibility that repeated inflammation associated with exposure to 
O3 over a lifetime may result in sufficient damage to respiratory 
tissue such that individuals later in life may experience a reduced 
quality of life, although such relationships remain highly uncertain.
    Studies of laboratory animals exposed to O3 have been 
relatively inconclusive with regard to genotoxicity and 
carcinogenicity, particularly at lower O3 concentrations. Only 
long-term exposure of laboratory animals to a high concentration of 
O3 (1.0 ppm) has been shown to evoke a limited degree of 
carcinogenic activity in one strain of female mice, whereas rats were 
unaffected. Furthermore, there was no concentration response 
relationship established, perhaps due to the limited scope of the 
studies, and there is inadequate information from other research to 
provide mechanistic support for the finding in mice. (For further 
discussion, see section V.C.9 in the Staff Paper.)
    Several epidemiologic studies cited in Section V.C.6 of the Staff 
Paper have attempted to find associations between daily mortality and 
O3 concentrations in various cities around the U.S. Although an 
association between ambient O3 exposure in areas with very high 
O3 levels and daily mortality has been suggested by these studies, 
the data are limited.
3. Adversity of Effects for Individuals
    Some population groups have been identified as being sensitive to 
effects

[[Page 65722]]

associated with exposures to ambient O3 levels, such that 
individuals within these groups are at increased risk of experiencing 
the above effects. Such groups at increased risk include active 
children and outdoor workers who regularly engage in outdoor activities 
that involve heavy levels of exertion during short-term periods of 
elevated ambient O3 levels or moderate levels of exertion during 
prolonged periods of elevated ambient O3 levels. Exertion 
increases the amount of O3 entering the airways and can cause 
O3 to penetrate to peripheral regions of the lung where lung 
tissue is more likely to be damaged. Secondly, individuals 
characterized as having preexisting respiratory disease (e.g., asthma 
or chronic obstructive lung disease), while not necessarily more 
responsive than healthy individuals in terms of the magnitude of 
pulmonary function decrements or symptomatic responses, may be at 
increased risk. That is, the impact of O3-induced responses on 
already-compromised respiratory systems may more noticeably impair an 
individual's ability to engage in normal activity or may be more likely 
to result in increased self-medication or medical treatment. It is 
recognized that limitations on using such individuals in experimental 
studies have prevented a more complete assessment of the full range of 
potential responses to O3 or their health significance in such 
individuals. Finally, some individuals are unusually responsive to 
O3 relative to other individuals with similar levels of activity 
or with a similar health status and may experience much greater 
functional and symptomatic effects from exposure to O3 than the 
average individual response. The mechanisms and characteristics 
responsible for increased sensitivity to O3 exposure have not been 
defined; thus, it is not clear whether these ``hyperresponders'' 
constitute a population subgroup with a specific risk factor or simply 
represent the upper end of the O3 response distributions within 
the general and at-risk populations.
    In making judgments as to when the effects discussed above become 
significant enough that they should be regarded as adverse to the 
health of individuals in these sensitive populations, the Administrator 
has looked to guidelines published by the American Thoracic Society 
(ATS) and the advice of CASAC. While recognizing that perceptions of 
``medical significance'' and ``normal activity'' may differ among 
physicians, lung physiologists, and experimental subjects, the ATS 
(1985) defined adverse respiratory health effects as ``medically 
significant physiologic or pathologic changes generally evidenced by 
one or more of the following: (1) Interference with the normal activity 
of the affected person or persons, (2) episodic respiratory illness, 
(3) incapacitating illness, (4) permanent respiratory injury, and/or 
(5) progressive respiratory dysfunction.'' Human health effects for 
which clear, causal relationships with exposure to O3 have been 
demonstrated (e.g., functional and symptomatic responses) fall into the 
first category listed in the ATS definition. Human health effects for 
which statistically significant associations have been reported in 
epidemiology studies fall into the second and third categories. These 
more serious effects include respiratory illness that may require 
medication (e.g., asthma), but not necessarily hospitalization, as well 
as emergency room visits and hospital admissions for acute occurrences 
of respiratory morbidity. Human health effects for which associations 
have been suggested but not conclusively demonstrated fall primarily 
into the last two categories. Evidence of these most serious health 
endpoints for O3 comes from studies of effects in laboratory 
animals, which can be extrapolated to humans only with a significant 
degree of uncertainty, and from human epidemiological studies.
    Application of these guidelines, in particular to the least serious 
category of effects related to ambient O3 exposures, involves 
judgments about which medical experts on the CASAC panel and public 
commenters have expressed a diversity of views. To help frame such 
judgments, the EPA staff defined gradations of individual functional 
responses (e.g., decrements in forced expiratory volume (FEV1), 
increased airway responsiveness) and symptomatic responses (e.g., 
cough, chest pain, wheeze), together with judgments as to the potential 
impact on individuals experiencing varying degrees of severity of these 
responses. These gradations and impacts, summarized below, are 
discussed in the Criteria Document (Chapter 9) and Staff Paper (section 
V.F, Table V-4a, 4b, 4c for individuals with impaired respiratory 
systems and Table V-5a, 5b, 5c for healthy individuals) and incorporate 
significant input from the CASAC panel of medical experts. The CASAC 
panel expressed a consensus view that these ``criteria for the 
determination of an adverse physiological response was reasonable'' 
(Wolff, 1995b).
    For individuals with impaired respiratory systems, small functional 
responses (e.g., FEV1 decrements of 3% to 10%, 
increased nonspecific bronchial responsiveness <100%, lasting less than 
4 hours) and/or mild symptomatic responses (e.g., cough with deep 
breath, discomfort just noticeable on exercise or deep breath, lasting 
less than 4 hours) would likely interfere with normal activity (and, 
therefore, be considered adverse under the ATS guidelines) for 
relatively few such individuals and would likely result in the use of 
normal medication as needed. Moderate functional responses (e.g., 
FEV1 decrements 10% but <20%, increased nonspecific 
bronchial responsiveness 300%, lasting up to 24 hours) and/
or moderate symptomatic responses (frequent spontaneous cough, marked 
discomfort on exercise or deep breath, wheeze accompanied by shortness 
of breath, lasting up to 24 hours) would likely interfere with normal 
activity for many such individuals and would likely result in 
additional or more frequent use of medication. Large functional 
responses (e.g., FEV1 decrements 20%, increased 
nonspecific bronchial responsiveness >300%, lasting longer than 24 
hours) and/or severe symptomatic responses (e.g., persistent 
uncontrollable cough, severe discomfort on exercise or deep breath, 
persistent wheeze accompanied by shortness of breath, lasting longer 
than 24 hours) would likely interfere with normal activity for most 
such individuals and would likely increase the likelihood of seeking 
medical treatment or visiting an emergency room.
    For active healthy individuals, it is judged that moderate levels 
of functional responses (e.g., FEV1 decrements >10% but <20% 
lasting up to 24 hours) and/or moderate symptomatic responses (e.g., 
frequent spontaneous cough, marked discomfort on exercise or deep 
breath, lasting up to 24 hours) would likely interfere with normal 
activity (and, therefore, be considered adverse under the ATS 
guidelines) for relatively few sensitive individuals in the at-risk 
populations of concern (active children and outdoor workers). Further, 
it is judged that large functional responses (e.g., FEV1 
decrements >20% lasting longer than 24 hours) and/or severe symptomatic 
responses (e.g., persistent uncontrollable cough, severe discomfort on 
exercise or deep breath, lasting longer than 24 hours) would likely 
interfere with normal activity for many sensitive individuals.
    In judging the extent to which such impacts represent effects that 
should be regarded as adverse to the health status of individuals, an 
additional factor that

[[Page 65723]]

the Administrator has considered is whether such effects are 
experienced repeatedly by an individual during the course of a year or 
only on a single occasion. While some experts would judge single 
occurrences of moderate responses to be a ``nuisance,'' especially for 
healthy individuals, a more general consensus view of the adversity of 
such moderate responses emerges as the frequency of occurrence 
increases. Thus, the Administrator agrees with the judgments presented 
in the Staff Paper that repeated occurrences of moderate responses, 
even in otherwise healthy individuals, may be considered to be adverse 
since they could well set the stage for more serious illness.

B. Human Exposure and Risk Assessments

    To put judgments about health effects that are adverse for 
individuals into a broader public health context, the Administrator has 
taken into account the results of human exposure and risk assessments. 
This broader context includes consideration, to the extent possible, of 
the size of particular population groups at risk for various effects, 
the likelihood that exposures of concern will occur for individuals in 
such groups under varying air quality scenarios, and the kind and 
degree of uncertainties inherent in assessing the risks involved. Such 
considerations provide a basis for judgments about the various levels 
of risk and the adequacy of public health protection afforded by the 
current NAAQS and alternative standards.
1. Exposure Analyses
    The EPA conducted exposure analyses to estimate O3 exposures 
for the general population and two at-risk populations, ``outdoor 
children'' and ``outdoor workers,'' living in nine representative U.S. 
urban areas. The areas include a significant fraction of the U.S. urban 
population, 41.7 million people, the largest areas with major O3 
nonattainment problems, and areas that are in attainment with the 
current NAAQS. Exposure estimates were developed for a recent year, as 
well as for modeled air quality that simulated conditions associated 
with attainment of the current NAAQS and various alternative standards. 
The exposure analyses provide estimates of the size of at-risk 
populations exposed to various concentrations under different 
regulatory scenarios, as presented in section V.G of the Staff Paper 
and summarized below. These estimates are an important input to the 
risk assessment summarized in the next section.
    The probabilistic NAAQS exposure model for O3 (pNEM/O3) 
used in these analyses builds on earlier deterministic versions of NEM 
by modeling random processes within the exposure simulation. The pNEM/
O3 model takes into account the most significant factors 
contributing to total human O3 exposure, including the temporal 
and spatial distribution of people and O3 concentrations 
throughout an urban area, the variation of O3 levels within each 
microenvironment, and the effects of exertion (which is represented by 
ventilation rate) on O3 uptake in exposed individuals. A more 
detailed description of pNEM/O3 and its application is presented 
in section V.G of the Staff Paper and associated technical support 
documents (Johnson et al., 1994; Johnson et al., 1996 a,b; McCurdy, 
1994a).
    The regulatory scenarios examined in the exposure analyses include 
1-hour O3 standards of 0.12 ppm (the current NAAQS) and 0.10 ppm, 
and 8-hour standards of 0.07, 0.08, and 0.09 ppm, the range of 
alternative 8-hour standards recommended in the Staff Paper and 
supported by CASAC as the appropriate range for consideration in this 
review. These analyses used 1- and 5-expected-exceedance forms of the 
standards and are based on use of a single year of data. These 
estimates were also used to roughly bound exposure estimates for other 
concentration-based forms of the standard under consideration (e.g., 
the second- and fifth-highest daily maximum 8-hour average O3 
concentration, averaged over a 3-year period) by using air quality 
analyses that compare alternative forms of the standard, as presented 
in Section IV and Appendix A of the Staff Paper. The estimated 
exposures reflect what would be expected in a typical or average year 
in an area just attaining a given standard over a 3-year compliance 
period. Additional air quality and exposure analyses were done to 
estimate the exposures that would be expected in the worst year of a 3-
year compliance period.
    The exposure estimates were done in terms of both ``people 
exposed'' (i.e., the number of people who experience a given level of 
air pollution, or higher, at least one time during the time period of 
analysis) and ``occurrences of exposure'' (i.e., the number of times a 
given level of pollution is experienced by the population of interest). 
Individual exposures were estimated in terms of dose, where dose is 
defined as the product of O3 concentration and ventilation rate 
over a defined period. Distributions of exposure estimates over the 
entire range of actual or simulated ambient O3 concentrations were 
developed as important input to the risk analysis, although results 
also were developed in terms of the frequency of exposures to ambient 
O3 concentrations above the lowest O3 concentrations at which 
health effects have been clearly associated with exposure to O3 in 
controlled human exposure studies (i.e., 0.12 ppm, 1-hour average, and 
0.08 ppm, 8-hour average, respectively).
    Key observations important in comparing estimated exposures 
associated with attainment of the current NAAQS and alternative 
standards under consideration include:
    (1) Children who are active outdoors (representing approximately 7% 
of the population in the study areas) appear to be the at-risk 
population group examined with the highest percentage and number of 
individuals exposed to O3 concentrations at and above which there 
is evidence of health effects, particularly for 8-hour average 
exposures at moderate exertion to O3 concentrations 
0.08 ppm.
    (2) On both an absolute number and a percentage basis, exposure 
estimates are higher for the 8-hour average effects level of 0.08 ppm 
at moderate exertion than for the 1-hour average effects level of 0.12 
ppm at heavy exertion.
    (3) Estimated exposures above these effects cutpoints, even on a 
percentage basis, vary significantly across the urban areas examined in 
this analysis. However, general patterns of exposure can be seen in 
comparing the current NAAQS and alternative standards, particularly in 
looking at the seven current nonattainment areas examined. For example, 
for estimates of the mean percent of outdoor children exposed to 8-hour 
average O3 concentrations 0.08 ppm while at moderate 
exertion, the following patterns are seen: the range of estimates 
associated with the current 1-hour NAAQS is approximately 1-21%, 
dropping to approximately <3% for a 0.10 ppm 1-hour standard. For 
alternative 8-hour standards (of the same 1-expected-exceedance form as 
the current NAAQS), the estimated ranges of mean percentages of outdoor 
children exposed are approximately 3-7% for a 0.09 ppm standard, 0-1.3% 
for a 0.08 ppm standard, and from essentially 0 in most areas to <0.1% 
for a 0.07 ppm standard.
    (4) In general, there are relatively small differences in comparing 
the distributions of 8-hour exposure estimates for outdoor children 
associated with 1- and 5-expected exceedance forms of any given 
alternative standard, although at particular cutpoints on the 
distribution,

[[Page 65724]]

differences between these two forms can appear to be significant in 
some areas.
    (5) Based on comparisons of air quality distributions, estimated 
exposures are generally comparable for 8-hour standards with 5-
expected-exceedance and fifth highest daily maximum concentration 
forms. In either case, exposure estimates for the worst year of a 3-
year compliance period would be higher than for the average or typical 
year, with the magnitude of the difference varying across areas. For 
example, for an 8-hour, 0.08 ppm standard of either form, about 95% of 
current nonattainment areas would have 10 or fewer exceedances of the 
0.08 ppm level in the worst year, compared to an average of less than 5 
exceedances in the typical year. Exposures estimated for a year in 
which there were 10 exceedances of the 0.08 ppm level would be roughly 
comparable to the exposures estimated to occur upon attainment in a 
typical year of a 0.09 ppm, 8-hour standard, with 1- to 5-expected-
exceedance forms.
    In taking these observations into account, the Administrator and 
CASAC recognize the uncertainties and limitations associated with such 
analyses, including the considerable, but unquantifiable, degree of 
uncertainty associated with a number of important inputs to the 
exposure model. A key uncertainty in model inputs results from the 
availability of only a limited human activity database, with regard to 
both the number of subjects who contributed daily activity diary data 
and the short time periods over which subjects recorded their daily 
activity patterns. These limitations may not adequately account for 
day-to-day repetition of activities common to children, such that the 
number of people who experience multiple occurrences of high exposure 
levels may be underestimated. Small sample size also limits the extent 
to which ventilation rates associated with various activities may be 
representative of the population group to which they are applied in the 
model. In addition, the air quality adjustment procedure used to 
simulate air quality distributions associated with attaining 
alternative standards, while based on statistical analyses of empirical 
data, incorporates significant uncertainty, especially when applied to 
areas requiring very large reductions in air quality to attain the 
alternative standards examined or to areas that are now in attainment 
with the current NAAQS. A more complete discussion of these 
uncertainties and limitations is presented in the Staff Paper and the 
technical support documents (Johnson et al., 1996a,b).
2. Risk Assessment
    The EPA conducted an assessment of health risks for several 
categories of respiratory effects associated with attainment of 
alternative 1- and 8-hour O3 NAAQS and under a recent year of air 
quality (``as is'' air quality). The O3 health risk assessment 
considers the same alternative air quality scenarios and the same nine 
urban areas that were examined in the human exposure analyses described 
above.
    The objective of the risk assessment was to estimate the magnitude 
of risks to population groups believed by EPA and CASAC to be at 
greatest risk either due to increased exposures (i.e., outdoor children 
and outdoor workers) or increased susceptibility (e.g., asthmatics) 
while characterizing, as explicitly as possible, the range and 
implications of uncertainties in the existing scientific database. 
While the risk estimates are subject to uncertainties as discussed 
below and should not be viewed as demonstrated health impacts, EPA 
believes they do represent reasonable estimates as to the possible 
extent of risk for these effects given the available information. 
Although it does not cover all health effects caused by O3, the 
risk assessment was intended as a tool, together with other information 
presented in the Staff Paper and in the revised Criteria Document, to 
aid the Administrator in judging which alternative O3 NAAQS would 
reduce risks sufficiently to protect public health with an adequate 
margin of safety.
    The health risk assessment builds upon the earlier O3 NAAQS 
health risk assessment work developed during the previous review of the 
standard. The health risk model takes into account (1) concentration-
response or exposure-response relationships used to characterize 
various respiratory effects of O3 exposure, (2) distributions of 
O3 1-hour and 8-hour daily maximum concentrations upon attainment 
of alternative NAAQS obtained from the pNEM/O3 analyses described 
above, and (3) distributions of population exposure, in terms of both 
the number of individuals in the general population, outdoor workers, 
and outdoor children exposed and the number of occurrences of exposure, 
upon attainment of alternative O3 NAAQS, obtained from the O3 
exposure analyses. A more detailed description of the risk assessment 
methodology and its application is presented in Section V.H of the 
Staff Paper and associated technical support document (Whitfield et 
al., 1996).

a. Adverse Lung Function and Respiratory Symptom Responses

    Risk estimates have been developed for several of the respiratory 
effects observed in controlled human exposure studies to be associated 
with O3 exposure. These include lung function decrements (measured 
as changes in FEV1) and moderate or severe pain on deep 
inspiration (PDI). Each of the effects is associated with a particular 
averaging time and, for most of the acute (1- to 8-hour) responses, 
effects also are estimated separately for specific ventilation ranges 
[measured as equivalent ventilation rate (EVR)] that correspond to the 
EVR ranges observed in the health studies used to derive exposure-
response relationships.
    An effect, or endpoint, can be defined in terms of a measure of 
biological response and the amount of change in that measure thought to 
be of concern. For lung function decrements, estimates are provided for 
the lower end, midpoint, and upper end of the range of response that 
might be considered an adverse health effect (i.e., 10, 15, 
or 20% FEV1 decrements) as discussed in II.A.3 above. For acute 
symptomatic effects, estimates are provided for responses that EPA 
considers to be of most concern (e.g., moderate and severe PDI). Due to 
limitations in the available data, the risk assessment provides 
estimates only for each individual health endpoint rather than various 
combinations of functional and symptomatic responses.
    The acute exposure-response relationships developed were based on 
the clinical studies and were applied to ``outdoor children,'' 
``outdoor workers,'' and the general population. While these specific 
clinical studies only included adults aged 18-35, findings from other 
clinical studies and summer camp field studies in at least six 
different locations in the northeast United States, Canada, and 
Southern California indicate changes in lung function in healthy 
children similar to those observed in healthy adults exposed to O3 
under controlled chamber conditions.
    While different risk measures are provided by the O3 health 
risk assessment, EPA has focused on ``headcount risk'' estimates. 
Headcount risk provides estimates of both the number of people affected 
and the number of incidences of a given health effect, considering 
individuals' personal exposures as they go about their daily activities 
(e.g., from indoors to outdoors, moving from place to place, and 
engaging in activities at different exertion levels).

[[Page 65725]]

    A major input to the headcount risk model is the series of 
population exposure distributions for the alternative NAAQS analyzed. 
Using available exposure estimates, risk estimates were calculated for 
the nine urban areas examined in the exposure analysis. For 8-hour 
exposures under moderate exertion, outdoor children represent the 
population group experiencing the greatest exposure, and, therefore, 
this population also has the highest risk estimates in terms of the 
percent of the population estimated to respond. Therefore, this summary 
of results focuses on the risk estimates for outdoor children. 
Whitfield et al. (1996) presents results of the headcount risk 
estimates for each of the nine urban areas for outdoor children and 
outdoor workers.
    Table 1 presents a summary of risk estimates for 8-hour and 1-hour 
health endpoints for outdoor children upon attainment of alternative 8-
hour, 1- and 5-expected exceedance standards and the current 0.12 ppm, 
1-hour standard. The risk estimates in Table 1 are for effects 
associated with exposure under moderate exertion. These risk estimates 
represent an aggregate estimate for the nine urban areas examined; an 
aggregate estimate is presented since there is significant variability 
in this risk measure across the areas. The uncertainty in these risk 
estimates associated with sample size considerations is characterized 
by the 90 percentile credible intervals shown.

  Table 1.--Percent of Outdoor Children Estimated to Experience Various Health Effects 1 or More Times per Year 
               Associated With 8- and 1-Hour Ozone Exposures Upon Attaining Alternative Standards*              
----------------------------------------------------------------------------------------------------------------
                Alternative standards                 Pulmonary function  Pulmonary function  Moderate or severe
-----------------------------------------------------  decrements, FEV1    decrements, FEV1      pain on deep   
                                                        15%      20%        inspiration   
          Level             Averaging time and form   associated with 8-  associated with 8-  associated with 1-
                                                        hour exposures      hour exposures      hour exposures  
----------------------------------------------------------------------------------------------------------------
0.07 ppm................  8-hour, 1 expected                         3.0       0.4 (0.1-1.8)      0.3 (0.01-1.9)
                           exceedance.                       **(1.0-6.6)                                        
0.08 ppm................  8-hour, 1 expected               5.1 (2.2-9.6)       1.4 (0.5-3.7)      0.6 (0.05-2.7)
                           exceedance.                                                                          
                          8-hour, 5 expected              6.7 (3.3-11.9)       2.3 (0.8-5.3)       0.8 (0.1-3.2)
                           exceedances.                                                                         
0.09 ppm................  8-hour, 1 expected              7.7 (3.3-13.3)       2.7 (1.0-6.1)       0.9 (0.1-3.5)
                           exceedance.                                                                          
                          8-hour, 5 expected              9.5 (5.1-15.9)       3.8 (1.5-7.9)       1.3 (0.2-4.2)
                           exceedances.                                                                         
0.12 ppm................  1-hour, 1 expected              8.3 (8.2-14.2)       3.0 (1.1-6.6)      1.0 (0.1-3.6) 
                           exceedance.                                                                          
----------------------------------------------------------------------------------------------------------------
* Estimates represent aggregate results for 9 urban areas examined. The total number of outdoor children        
  residing in the 9 urban areas was 3.1 million.                                                                
** 90% credible interval.                                                                                       

    Key observations important in comparing estimated health risks 
associated with attainment of the current NAAQS and alternative 
standards under consideration include:
    (1) On both an absolute number and a percentage basis, risk 
estimates are higher for effects associated with 8-hour exposures under 
moderate exertion than for effects associated with 1-hour exposures 
under heavy exertion.
    (2) Reflecting a continuum of risk, there is a decreasing trend in 
the median estimates of the population estimated to experience the lung 
function and symptomatic responses as one moves along the range of 
alternative 8-hour average, 1-expected exceedance standards under 
consideration. For example, based on the aggregate risk estimates 
summarized in Table 1, the median percent of outdoor children estimated 
to experience FEV1 decrements greater than 15% is reduced from 
about 7.7% for a 0.09 ppm, 8-hour standard to about 5.1% for a 0.08 
ppm, 8-hour standard. Attaining a 0.07 ppm, 8-hour standard results in 
a further reduction to about 3.0% of outdoor children estimated to 
experience this effect.
    (3) In general, the differences in risk estimates for outdoor 
children associated with 1- and 5-expected exceedance standards set at 
the same standard level are relatively modest within the continuum of 
risk. For example, the risk estimates for lung function decrements 
15% associated with a 5-expected exceedance standard set at 
0.08 ppm fall between the risk estimates for the 0.08 and 0.09 ppm, 1-
expected exceedance, 8-hour standards. Similarly, the risk estimates 
for a 5-expected exceedance standard set at 0.09 ppm fall between the 
risk estimates for the 0.09 and 0.10 ppm, 1-expected exceedance, 8-hour 
standards. The risk estimates for the current 0.12 ppm, 1-hour standard 
fall between the risk estimates for the 0.09 ppm, 1- and 5-expected 
exceedance standards.
    (4) Multiple occurrences of lung function decrements 15% 
and 20% associated with 8-hour exposures under moderate 
exertion are estimated to occur for outdoor children upon attainment of 
any of the alternative 1- or 8-hour standards analyzed. The average 
seasonal numbers of occurrences per responder across the urban areas 
included in the analysis range from four to about nine for lung 
function decrements 15% and from two to about five for lung 
function decrements   >20%, such that some individuals will experience 
more frequent occurrences of effects during the O3 season, whereas 
others will experience fewer occurrences than the average in any given 
area.
    (5) Based on comparisons of air quality distributions, risk 
estimates are generally comparable between 8-hour standards with 5-
expected exceedances or fifth-highest daily maximum concentration 
forms. As noted in the previous discussion of the exposure estimates, 
for either form the worst year of a 3-year compliance period would be 
higher than for the average or typical year. For example, about 95% of 
current nonattainment areas meeting either form of an 8-hour, 0.08 ppm 
standard would have 10 or fewer exceedances in the worst year, compared 
to an average of less than five exceedances in a typical year. Risk 
estimates for a year in which there were 10 exceedances of 0.08 ppm, 8-
hour average vary from urban area to urban area but fall between the 
risk estimates for a 5-expected exceedance standard of 0.08 ppm and a 
5-expected exceedance standard set at 0.09 ppm.
    The EPA believes, and CASAC concurred, that the models selected to 
estimate exposure and risk are appropriate and that the methods used to 
conduct the health risk assessment represent the state of the art. 
Nevertheless, the Administrator and CASAC recognize that there are many 
uncertainties inherent in such analyses. The resulting ranges of 
quantitative risk

[[Page 65726]]

estimates do not reflect all of the uncertainties associated with the 
numerous assumptions inherent in such analyses (Wolff, 1995b). Some of 
the most important caveats and limitations concerning the health risk 
assessment for lung function and respiratory symptom endpoints include: 
(1) The uncertainties and limitations associated with the exposure 
analyses discussed above, (2) the extrapolation of exposure-response 
functions below the lowest-observed-effects levels to an estimated 
background level of 0.04 ppm, and (3) the inability to account for some 
factors which are known to affect the exposure-response relationships 
(e.g., assigning children the same symptomatic response rates as 
observed for adults and not adjusting response rates to reflect the 
increase and attenuation of responses that have been observed in 
studies of lung function and symptoms upon repeated exposures). A more 
complete discussion of assumptions and uncertainties is contained in 
the Staff Paper and in the technical support document (Whitfield et 
al., 1996).

b. Excess Respiratory-Related Hospital Admissions

    As discussed earlier in this notice, several epidemiology studies, 
mainly conducted in the northeastern portion of the U.S. and 
southeastern Canada, have reported excess daily respiratory-related 
hospital admissions associated with elevated O3 levels during the 
O3 season. To gain insight into the possible impact of just 
attaining alternative 1- and 8-hour O3 standards, EPA has 
developed a risk model for this endpoint. The model is based on the 
regression coefficient (and the corresponding standard error) developed 
by Thurston et al. (1992) for New York City and estimated daily maximum 
hourly average O3 levels over an entire season at various monitors 
in New York City upon attainment of alternative standards (as developed 
for the pNEM/O3 analysis). The regression coefficient (11.7 
admissions/ppm O3/106 people) and its standard error (4.7 
admissions/ppm O3/106 people) were used to define a 
probabilistic concentration-response relationship. The model is 
described in more detail in Whitfield et al. (1996). One-hour daily 
maximum O3 concentrations for one O3 season under various 
alternative air quality standards were used to estimate the number of 
excess respiratory-related admissions of asthmatics (i.e., those 
attributable to O3 concentrations higher than background). The 
O3 concentration-response relationship developed by Thurston et 
al. (1992) was based on air quality data from the Queens monitor. 
Therefore, the risk estimates based on the Queens County monitor most 
closely represent the air quality index used in the original study and 
are summarized below. In each analysis, the air quality was adjusted to 
just attaining a particular standard at the monitor with the highest 
O3 levels for the New York area, and the O3 levels were 
adjusted at the other monitors using the procedures described in 
Johnson et al. (1996a).
    Based on Table V-20 in the Staff Paper, the hospital admissions 
model results in a median estimate of excess respiratory-related 
admissions for asthmatic individuals attributable to O3 exposure 
of approximately 390 (with a 90% credible interval of approximately 
130-640) per year for the New York City area based on ``as is'' air 
quality using 1991 data. Just attaining the current 0.12 ppm, 1-hour 
standard is estimated to reduce excess hospital admissions to about 210 
(with a 90% credible interval of 70-340), which is approximately a 50% 
decrease in O3-induced admissions due to concentrations in excess 
of the estimated 0.04 ppm estimated background level. Upon attaining 
the 0.08 ppm, 8-hour, 1 expected exceedance standard, for example, the 
median estimate for excess respiratory-related hospital admissions 
attributable to O3 exposure is further reduced to approximately 
115 (with a 90% credible interval of approximately of 40-190). This 
represents a 70% decrease in O3-induced hospital admissions from 
the ``as is'' scenario and about a 45% decrease from the current 1-hour 
standard.
    It should be recognized that the O3-induced excess hospital 
admissions represent a relatively small fraction of the overall 
respiratory-related hospital admissions for asthmatics over the seven 
month O3 season. Based on an estimated 15,000 admissions per year 
during the O3 season, the reduction in hospital admissions for 
asthmatics for any respiratory-related reason in going from ``as is'' 
air quality to attaining a 0.08 ppm, 8-hour, 1-expected exceedance 
standard is about 2%. Similarly, the reduction from attaining the 
current 1-hour standard to attaining a 0.08 ppm, 8-hour, 1-expected 
exceedance standard represents about a 0.6% decrease in total 
respiratory admissions for asthmatics due to all causes.
    Key observations important in comparing hospital admission risk 
estimates associated with attainment of the current NAAQS and 
alternative standards under consideration include:
    (1) Risk estimates for excess hospital admissions for asthmatics 
attributable to O3 exposures in excess of an estimated background 
level of 0.04 ppm are projected to be significantly reduced (about 45%) 
under a 0.08 ppm, 8-hour, 1-expected exceedance standard compared to 
the current 1-hour NAAQS.
    (2) The excess hospital admissions risk estimates associated with 
1- and 5-expected exceedance standards set at 0.08 ppm are very 
similar.
    (3) When viewed from the perspective of respiratory-related 
admissions for asthmatics due to all causes, the excess hospital 
admissions attributable to O3 exposures in excess of an estimated 
background concentration of 0.04 ppm constitute a relatively small 
portion of total admissions. For example, comparing the risk estimates 
associated with the current 1-hour NAAQS and a 0.08 ppm, 8-hour, 1-
expected exceedance standard results in only about a 0.6% reduction in 
respiratory hospital admissions for asthmatics due to all causes.
    In taking these observations into account, the Administrator 
recognizes the uncertainties and limitations associated with the 
hospital admission risk assessment. These include: (1) The inability at 
this time to quantitatively extrapolate the risk estimates for the New 
York City area to other urban areas, (2) uncertainty associated with 
the underlying epidemiological study that served as the basis for 
developing the concentration-response relationship used in the 
analysis, and (3) uncertainties associated with the air quality 
adjustment procedure used to simulate attainment of alternative 
standards for the New York City area. A more complete discussion of 
these uncertainties and limitations is presented in the Staff Paper and 
technical support document (Whitfield et al., 1996).

c. Conclusions on the Elements of the Primary Standard

    In selecting a primary standard for O3, the Administrator must 
specify: (1) Averaging time, (2) O3 concentration (i.e., level), 
and (3) form (i.e., the air quality statistic to be used as a basis for 
determining compliance with the standard).5 All three of these 
elements are necessary to define a standard. Based on the assessment of 
relevant scientific and technical information in the Criteria Document, 
section VI of the Staff Paper outlines a number of key factors to be 
considered in specifying each of these elements, as well as 
recommendations to focus consideration on a discrete range of options 
for each

[[Page 65727]]

element. The factors reflect an integration of information on acute and 
chronic health effects associated with exposure to ambient O3; 
expert judgments on the adversity of such effects for individuals; and 
policy judgments, informed by air quality analyses and quantitative 
risk assessment when possible, as to the point at which risks would be 
reduced sufficiently to achieve protection of public health with an 
adequate margin of safety.
---------------------------------------------------------------------------

    \5\ This review focused only on a standard for O3, as the 
most appropriate surrogate for photochemical oxidants.
---------------------------------------------------------------------------

    This approach to selecting a proposed primary standard was endorsed 
by members of CASAC (Wolff, 1995b), particularly through their advice 
to the Administrator that ``EPA's risk assessments must play a central 
role in identifying an appropriate level'' and their recognition that 
the selection of a specific concentration and form ``is a policy 
judgment.'' Further, it was the consensus view of CASAC that the ranges 
of levels (0.07 to 0.09 ppm) and forms (1 to 5 exceedances) recommended 
in the Staff Paper were appropriate.
    Thus, the Administrator has focused her consideration on the 
recommended options and key factors outlined in the Staff Paper. The 
considerations that were most influential in the Administrator's 
selection of each specific element of the proposed standard are 
outlined below.
1. Averaging Time
    The Administrator concurs with the unanimous recommendation of 
CASAC (Wolff, 1995b) ``that the present 1-hr standard be eliminated and 
replaced with an 8-hr standard,'' and that more research is needed to 
resolve uncertainties about potential chronic effects before 
appropriate consideration can be given to establishing a long-term 
(e.g., seasonal or annual) standard. These judgments are supported by 
the following key observations and conclusions:
    (1) The 1-hour averaging time specified in the current NAAQS was 
originally selected primarily on the basis of health effects associated 
with short-term (i.e., 1- to 3-hour) exposures, with qualitative 
consideration given to preliminary information on potential 
associations with longer exposure periods.
    (2) Substantial new health effects information available for 
consideration in this review demonstrates associations between a wide 
range of health effects and prolonged (i.e., 6- to 8-hours) exposures 
below the level of the current 1-hour NAAQS.
    (3) Results from the quantitative risk analyses show that attaining 
a standard with a 1-hour averaging time reduces the risk of 
experiencing health effects associated with both 1-hour and 8-hour 
exposures. Likewise, attaining an 8-hour standard reduces the risk of 
experiencing health effects associated with both 8-hour and 1-hour 
exposures. Thus, reductions in risks from both short-term and prolonged 
exposures can be achieved through a primary standard with an averaging 
time of either 1 or 8 hours. As a result, establishment of both 1-hour 
and 8-hour standards would not be necessary to reduce risks associated 
with the full range of observed acute health effects.
    (4) The 8-hour averaging time is more directly associated with 
health effects of concern at lower O3 concentrations than is the 
1-hour averaging time. It was thus the consensus of CASAC ``that an 8-
hr standard was more appropriate for a human health-based standard than 
a 1-hr standard.'' (Wolff, 1995b)
    (5) While there is a large animal toxicology database providing 
clear evidence of associations between long-term (e.g., from several 
months to years) exposures and lung tissue damage, with additional 
evidence of reduced lung elasticity and accelerated loss of lung 
function, there is not corresponding evidence for humans. Moreover, the 
state of the science has not progressed sufficiently to permit 
quantitative extrapolation of the animal-study findings to humans. 
Thus, the Administrator concludes that consideration of a separate 
long-term O3 standard is not appropriate at this time. As 
discussed below, however, the Administrator has considered the 
possibility of long-term effects in selecting the level of the 
standard, which will provide protection against such effects to the 
extent they may occur in humans, by lowering overall air quality 
distributions and, thus, reducing cumulative long-term exposures.
2. Level
    The Administrator's consideration of an appropriate level for an 8-
hour standard to protect public health with an adequate margin of 
safety necessarily reflects a recognition, as emphasized by CASAC, that 
it is likely that ``O3 may elicit a continuum of biological 
responses down to background concentrations'' (Wolff, 1995b). Thus, in 
the absence of any discernible threshold, it is not possible to select 
a level below which absolutely no effects are likely to occur. Nor does 
it seem possible, in the Administrator's judgment, to identify a level 
at which it can be concluded with confidence that no ``adverse'' 
effects are likely to occur. In such a case, as CASAC has advised, the 
traditional paradigm for standard-setting cannot be applied in the 
usual way, and assessments of risk ``must play a central role in 
identifying an appropriate level'' (Wolff, 1995b). Thus, the 
Administrator's task becomes one of attempting to select a standard 
level that will reduce risks sufficiently to protect public health with 
an adequate margin of safety, since a zero-risk standard is neither 
possible nor required by the Act. Consequently, as CASAC recognized, 
``the selection of a specific level * * * is a policy judgment'' 
(Wolff, 1995b). The Administrator's policy judgment on the level of the 
proposed standard is framed by the above considerations and informed by 
the following key observations and conclusions:
    (1) During the last review of the O3 criteria and standards, 
the CASAC concluded that the existing 1-hour standard set at 0.12 ppm 
O3 provided ``little, if any, margin of safety,'' and the upper 
end of the range of consideration for a 1-hour standard should be 0.12 
ppm (McClellan, 1989). In addition, several members of the CASAC panel 
recommended that consideration should be given to a lower 1-hour level 
of 0.10 ppm to offer some protection against effects for which there 
was preliminary information at that time of associations with 8-hour 
exposures to O3.
    Regarding currently available evidence of O3-related effects:
    (2) Based on a significant body of information available since the 
last review, there is now clear evidence from human clinical studies 
that O3 effects of concern are associated with the 8-hour 
exposures tested. Studies were done at 8-hour exposure levels of 0.12, 
0.10, and 0.08 ppm). This includes evidence of the following 
statistically significant responses at 6- to 8-hour exposures to the 
lowest concentration evaluated, 0.08 ppm O3, at moderate exertion: 
lung function decrements, respiratory symptoms (e.g., cough, pain on 
deep inspiration), nonspecific bronchial responsiveness, and 
biochemical indicators of pulmonary inflammation. Field studies provide 
evidence of similar functional and symptomatic effects at ambient 
O3 exposures that are consistent with the clinical findings. 
Laboratory animal studies provide supporting evidence of O3-
induced biochemical indicators of inflammation and functional changes.
    (3) Numerous epidemiological studies have reported excess hospital 
admissions and emergency department visits for respiratory causes (for 
asthmatic individuals and the general population) attributed primarily 
to ambient O3 exposures, including O3

[[Page 65728]]

concentrations below the level of the current standard, with no 
discernible threshold at or below this level. The biological 
plausibility of attributing such effects to ambient O3 exposures 
is supported by human studies showing increased nonspecific bronchial 
responsiveness, laboratory animal studies showing pulmonary changes 
that decrease the effectiveness of the lung's defenses against 
bacterial respiratory infections, and the reasonable anticipation that 
O3 exposures also increase the risk of respiratory infections in 
humans, based on the many similarities between animal and human defense 
mechanisms.
    (4) Long-term laboratory animal studies suggest that changes in 
lung biochemistry and structure may, under certain circumstances, 
become irreversible, although it is unclear whether long-term exposures 
to ambient O3 levels result in similar chronic health effects in 
humans.
    Regarding the types and severity of O3-induced physiological 
effects that are considered to be adverse to the health status of 
individuals experiencing such effects:
    (5) With regard to lung function decrements and respiratory 
symptoms, the Administrator recognizes that these O3-induced 
effects are transient and reversible, and concludes that the extent to 
which such effects are adverse to the health status of an individual 
depends upon the severity, duration, and frequency with which an 
individual experiences such effects throughout the O3 season. 
While group mean responses in clinical studies at the lowest exposure 
level tested of 0.08 ppm are typically small or mild in nature, 
responses of some extremely sensitive individuals are sufficiently 
severe and extended in duration to be considered adverse. This would 
especially be true to the extent that those individuals likely to 
experience such effects would, on average, experience them several 
times a year.
    (6) With regard to increased hospital admissions and emergency room 
visits, the Administrator judges that such effects are clearly adverse 
to individuals.
    (7) With regard to pulmonary inflammation, the Administrator 
recognizes that singular occurrences of inflammation are likely 
reversible and potentially of little health significance. On the other 
hand, repeated inflammatory responses associated with exposure to 
O3 over a lifetime have the potential to result in damage to 
respiratory tissue such that individuals later in life may experience a 
reduced quality of life. Furthermore, there is the possibility that 
repeated pulmonary inflammatory responses could adversely affect 
asthmatic individuals by resulting in increased medication use, medical 
treatment, and/or emergency room visits and hospital admission.
    Accordingly, the Administrator judges that repeated exposures to 
O3 levels that produce inflammation of the lungs are adverse to 
individuals likely to experience such exposures over long periods of 
time.
    The Administrator has considered the results of the exposure and 
risk analyses and the following key observations and conclusions from 
these analyses in putting effects considered to be adverse to 
individuals into a broader public health perspective and making 
judgments about the level of a standard that would reduce risk 
sufficiently to protect public health with an adequate margin of 
safety:
    (8) The median risk estimates for functional and symptomatic 
effects, as well as for excess hospital admissions and emergency room 
visits due to respiratory causes, are approximately the same or only 
marginally smaller for some of the 0.09 ppm 8-hour standard options 
evaluated (including those with forms ranging from 1- to 3-expected-
exceedances 6) as compared to the current 0.12 ppm 1-hour NAAQS 
(risk estimates are somewhat larger for a 0.09 ppm 8-hour 5-expected-
exceedance form as compared to the current NAAQS).
---------------------------------------------------------------------------

    \6\ Based on air quality comparisons, since risk estimates are 
only currently available for the 1- and 5-expected-exceedance forms 
of a 0.09 ppm standard.
---------------------------------------------------------------------------

    (9) Within any given urban area, statistically significant 
reductions in exposure and risk associated with functional and 
symptomatic effects result from alternative 8-hour standards as the 
level changes from 0.09 ppm to 0.08 ppm to 0.07 ppm. These reductions 
represent differences of hundreds of thousands of times that children 
would likely experience such effects under the range of alternative 
standards considered relative to the current standard.7 There are 
significant uncertainties in such quantitative estimates, however, and 
there is no break point or bright line that differentiates between 
acceptable and unacceptable risks within this range.
---------------------------------------------------------------------------

    \7\ With regard to these risk analyses, CASAC concluded ``that 
there is no `bright line' which distinguishes any of the proposed 
standards (either the level or the number of allowable exceedances) 
as being significantly more protective of public health,'' and noted 
that the differences in percent of outdoor children responding 
between the present standard and the most stringent standard ``are 
small and their ranges overlap for all health endpoints.'' (Wolff, 
1995b) To address any apparent differences between EPA's and CASAC's 
conclusions, it is important to note that EPA's risk analysis report 
(Whitfield et al., 1996) makes clear that there are statistically 
significant differences in estimated risk for alternative standard 
levels; whether one judges the differences to be significant or 
small can depend on whether one focuses on percentages, as CASAC's 
letter did, or on total numbers of times that children or other at-
risk individuals experience such effects. The overlap in the ranges 
of risk referred to in the CASAC letter reflect differences among 
cities used in EPA's risk analysis (e.g., air quality, esposure 
patterns, environmental factors), not random uncertainties in risk 
estimates within any given city. Thus, the fact that the ranges 
overlap does not mean that there are no real or statistically 
significant differences in protection among alternative standards.
---------------------------------------------------------------------------

    (10) Similarly, reductions in hospital admissions and emergency 
room visits for asthmatic individuals are estimated to occur with each 
change in the level of the standard from 0.09 ppm to 0.08 ppm to 0.07 
ppm. However, hospital admissions for asthmatic individuals associated 
with ambient O3 exposures within the range of standard levels 
under consideration represent a relatively small fraction of the total 
respiratory-related hospital admissions for asthmatics over the O3 
season.
    (11) Estimated exposures to O3 concentrations 0.08 
ppm (at which increased nonspecific bronchial responsiveness, decreased 
pulmonary defense mechanisms, and indicators of pulmonary inflammation 
have been observed in humans) are essentially zero at the 0.07 ppm 
standard level for most areas evaluated in the exposure analyses for 
the at-risk population of outdoor children. Such exposures of outdoor 
children increase to approximately 0 to 1.3% at the 0.08 ppm level, 
while the estimated range at the 0.09 ppm level rises to 3-7% for the 
areas evaluated.
    (12) While recognizing that extremely sensitive individuals may 
experience adverse but transient effects with a standard set at 0.08 
ppm, no CASAC panel member supported selection of 0.07 ppm as the level 
of a primary standard. Of the members who expressed their personal 
views, three indicated a preference for a level of 0.08 ppm, one for a 
range of 0.08 to 0.09 ppm, three for a level of 0.09 ppm (with one of 
the three expressing a preference for selecting a form that would 
result in equivalent protection to the current standard), and one for a 
range of 0.09 to 0.10 ppm, associated with public advisories for 
O3 levels at and above 0.07 ppm. Other CASAC panel members also 
expressed support for such public notices or advisories reflecting 
potential effects for extremely sensitive individuals associated with 
O3 levels as low as 0.07 ppm.

[[Page 65729]]

    After carefully assessing the key observations and conclusions 
drawn from the available scientific evidence and analyses, and taking 
into account the advice of CASAC and comments from the public, the 
Administrator focused her consideration on two policy options for the 
level of the primary O3 standard: 0.08 ppm and 0.09 ppm. A 
standard set at a level of 0.09 ppm (within the middle of the range of 
forms discussed below) would result in approximately equivalent public 
health protection as that afforded by the current standard; a 0.08 ppm 
level would provide greater protection. In her judgment, the selection 
of either level could properly take into account the available 
scientific and technical information and would be consistent with the 
views expressed by her scientific advisors, since none of the CASAC 
panel members expressed the view that the standard level should be set 
below 0.08 ppm. On the other hand, the Administrator is aware of 
alternative views that place great weight on margin of safety 
considerations, leading to support by some commentors for a standard 
level option of 0.07 ppm, as discussed further below.
    In deciding between the 0.08 ppm and 0.09 ppm alternatives, the 
Administrator took into account several factors including: (1) 
Estimates of risk, in terms of the percentage of children likely to 
experience respiratory symptoms and decreases in lung function of 
concern; (2) estimates of exposures to the lowest concentration at 
which other, more uncertain effects have been observed; and (3) the 
body of health effects evidence as a whole.
    In considering risk estimates, she noted that there is a continuum 
of increasing risk reduction in going from the upper end of the range 
of consideration (0.09 ppm, with a 5-expected-exceedance form) down to 
the lower end of this range (0.08 ppm, with a 1-expected-exceedance 
form) and below, and that the current 1-hour standard provides a level 
of protection within but near the top of this range. These quantitative 
risk estimates are summarized in Table 1 above, showing the varying 
percentages of children estimated to experience these symptomatic and 
functional effects of concern for the alternative 0.08 and 0.09 ppm 8-
hour standards. Quantitative risks could be estimated for these effects 
because studies are available that allow for a determination of how the 
percentages of individuals likely to experience such effects vary as a 
function of the O3 concentrations to which they are exposed.
    With respect to exposure estimates, she noted that these 
alternative standards provide differing degrees of protection from 
exposures to O3 concentrations that have been associated with 
other potentially adverse, but more uncertain effects, including 
nonspecific bronchial responsiveness (related, for example to 
aggravation of asthma) and inflammation of the lungs (related to 
potential chronic aggravation of bronchitis or long-term damage to the 
lungs). For these effects, the evidence is not sufficient to conduct a 
quantitative risk assessment, but the relative protection of the 
alternative standards can be considered in terms of the percentages of 
outdoor children who would be exposed one or more times to the lowest 
concentration at which evidence of these effects has been observed 
(i.e., 0.08 ppm). As noted above, in summarizing key observations from 
the exposure assessment, the percentages of outdoor children likely to 
be exposed to the level are approximately 3 to 7% for a 0.09 ppm 
standard (with a 1-expected-exceedance form) and approximately 0 to 
1.3% for a 0.08 ppm standard with the same form. For comparison, these 
exposures range from approximately 1 to 21% for the current 1-hour 
standard of 0.12 ppm,8 dropping to essentially 0% for a 0.07 ppm 
8-hour standard. While the public health risks associated with these 
effects are uncertain and cannot be assessed definitively, the 
Administrator finds these different exposures to be an important factor 
in making this policy choice.
---------------------------------------------------------------------------

    \8\ The wide range of exposures for this 1-hour standard 
(compared to the narrower ranges for the 8-hour standards) reflects 
much greater variability across cities in the extent to which a 1-
hour standard limits 8-hour exposures.
---------------------------------------------------------------------------

    Both the quantitative risk estimates for respiratory symptoms and 
decreased lung function and the exposure estimates associated with 
bronchial responsiveness and inflammation of the lung provide an 
important perspective in assessing the public health implications of 
effects observed in individuals exposed to various O3 
concentrations. Nonetheless, the Administrator believes that these 
estimates alone do not provide a clear basis for making a policy choice 
between the 0.09 and 0.08 ppm levels for an 8-hour standard.
    Finally, the Administrator noted that in a number of clinical 
studies examining all of the effects discussed above in human subjects, 
various researchers have consistently reported statistically 
significant effects at an exposure level of 0.08 ppm. This exposure 
level reflects the lowest level that researchers have chosen to conduct 
the relevant studies, and it does provide a strong point of consistency 
in the currently available scientific evidence. Effects at this level 
observed in clinical studies are also consistent with the results of 
epidemiological and summer camp studies reporting similar symptomatic 
and functional effects associated with exposures to ambient levels of 
O3 that broadly span this clinical lowest-observed-effects level.
    The Administrator has weighed the importance of increased 
protection for those extremely sensitive individuals who may experience 
symptomatic and functional effects at lower O3 concentrations than 
the population as a whole, the uncertainties in considering the 
potentially more serious but as yet uncertain chronic effects. For all 
these reasons, the Administrator is proposing to set the level of an 8-
hour O3 standard at 0.08 ppm.
    However, as noted above, in making this judgment, the Administrator 
is mindful that a range of views has been expressed as to the 
appropriate policy choice between 0.08 ppm and 0.09 ppm for an 8-hour 
standard level. For example, while some CASAC members supported the 
choice of the proposed 0.08 ppm, fully half or more of the CASAC panel 
members expressing views on a specific level supported a specific level 
or range of levels that include 0.09 ppm.
    Those that favored a 0.09 ppm standard did so on the basis of 
several kinds of judgments. As the CASAC noted, it is unclear whether 
there is a threshold level for the various health effects discussed 
above. For this reason, some CASAC members and others have suggested 
that it is difficult to determine if a margin of safety exists for any 
particular level and therefore, in their opinion the differences in 
health protection may not be significant enough to justify a change 
from the current standard.
    Others may support a 0.09 ppm standard on the basis of 
uncertainties about: (1) The medical significance of the reported 
effects of O3 exposure at these levels for individuals 
experiencing such effects; (2) the public health significance of the 
degree of exposure and risk reduction likely to be achieved by moving 
from 0.09 ppm O3 to 0.08 ppm O3; (3) the appropriate weight 
to be given to the health endpoints that could not be addressed in the 
quantitative risk assessment; and 4) how to address the various 
uncertainties in the scientific evidence on health effects and in the 
exposure and risk estimates in making a policy decision on a standard 
level

[[Page 65730]]

that will protect public health with an adequate margin of safety.
    A policy decision to set a 0.09 ppm 8-hour standard would place 
more weight on the transient and reversible nature of reported 
decrements in lung function, increased respiratory symptoms, and lung 
inflammation, and would call into question the medical significance of 
moderate levels of such effects, particularly for healthy individuals. 
This view would also emphasize the relatively small fraction of the 
overall respiratory-related hospital admissions for asthmatics that are 
estimated to be linked to O3 exposures over the O3 season. 
Thus, it could be reasonable to judge that any incremental reduction in 
such risk achieved by levels below 0.09 ppm O3 would be of little 
consequence when viewed from a broader public health perspective. 
Further, this view would note the lack of evidence linking O3-
induced markers of inflammation and cell damage with chronic 
respiratory damage in humans. In this view, while the potential for 
O3-induced chronic respiratory damage would be a matter of public 
health concern, additional research would be needed before such 
concerns should be reflected in margin of safety considerations. These 
interpretations of the evidence and judgments as to the nature and 
significance of the reported O3-induced health effects, could 
justify a judgement that an 8-hour standard set at 0.09 ppm O3 
protects public health with an adequate margin of safety. Thus, the 
Administrator solicits public comment on this alternative of a 0.09 ppm 
level for an 8-hour standard.
    In sharp contrast, the Administrator also notes that others would 
make a different set of judgments as to the significance of O3-
induced health effects and the appropriate public health policy 
response. To reflect these views, the Administrator is also requesting 
comment on the alternative of establishing the level of an 8-hour 
standard at 0.07 ppm. A standard set at this level, within a range of 
forms (as discussed in the next section), would be highly precautionary 
in nature. A policy decision to select such a standard would reflect an 
emphasis on (1) The many studies that have reported observed effects in 
humans at moderate levels of exercise at an exposure level of 0.08 ppm; 
(2) judgments that the reported decrements in lung function, increased 
respiratory symptoms, and indicators of inflammation, even when 
transient and reversible at moderate levels, are adverse effects; and 
(3) judgments that even the most sensitive responders should be 
afforded protection against the occurrence of such effects through 
national ambient air quality standards. This view would judge that even 
a relatively small number of O3-induced excess hospital admissions 
do pose a significant public health problem, especially considering 
that for every hospital admission, there are likely many more patients 
visiting physicians and an increasing use of medication. Further, even 
though no clear linkage has been established between the O3-
induced markers of inflammation, cell damage, and chronic respiratory 
damage shown in animal toxicological studies and similar effects in 
humans, this view would hold that the possibility of such a link 
suggests the need for a wide margin of safety.
    Based on these judgments as to the nature and significance of the 
reported O3-induced health effects, some commentors would reach 
the policy judgment that an 8-hour standard should be set at 0.07 ppm 
to protect public health with an adequate margin of safety. In 
recognition of this view, the Administrator also solicits public 
comment on an 0.07 ppm level for an 8-hour standard.
    Based on the comments received and the accompanying rationale, the 
Administrator may choose at the time of final promulgation to adopt a 
standard from within the range of alternatives on which she is 
requesting comment, with further specification of the form of such a 
standard (as discussed in the next section), in lieu of the 0.08 ppm 
level of the 8-hour O3 standard she is proposing today.
3. Form
    The current primary NAAQS is expressed in a ``1-expected-
exceedance'' form. That is, the standard is formulated on the basis of 
the expected number of days per year, on average, on which the level of 
the standard will be exceeded. More specifically, the test for 
determining attainment of the standard specifies that the expected 
number of days per year on which the level is exceeded is to be less 
than or equal to 1.0 (values equal to or greater than 1.05 round up), 
averaged over a three year period, and that specific adjustments are to 
be made for missing data. The current NAAQS is applied on a site-by-
site basis; data from multiple air quality monitoring sites are not 
combined.
    Since promulgation of the current NAAQS in 1979, a number of 
concerns have been raised about the 1-expected-exceedance form. These 
include, in particular, the year-to-year stability of the number of 
exceedances, the stability of attainment status of an area, the data 
handling conventions, including the procedures for adjusting for 
missing data, and the evaluation of air quality on a site-by-site basis 
rather than some form of averaging across monitoring sites. These 
issues are discussed in some detail in section V.I of the Staff Paper, 
and alternative forms that would address such issues are recommended 
for consideration.
    In evaluating alternative forms for the primary standard, the 
adequacy of the public health protection provided is of foremost 
consideration. However, consistent with the advice of CASAC, the 
Administrator is also interested in considering alternative forms that 
provide increased stability and thereby reduce the likelihood of areas 
``flip-flopping'' in and out of attainment simply as a result of 
natural variability in meteorological conditions that are conducive to 
O3 formation. Such instability can have the effect of reducing 
public health protection by disrupting ongoing implementation plans and 
associated control programs.
    Based on information presented in sections IV and V.I of the Staff 
Paper and the advice of CASAC, the Administrator has focused her 
consideration on the following alternatives:
    (1) Revising the current 1-expected-exceedance form of the standard 
to allow for multiple (up to five) expected exceedances per year, 
averaged over three years. A multiple-exceedance form would be based on 
a less extreme air quality statistic and, thus, would increase the 
stability of the expected-exceedance form.
    (2) Adopting a concentration-based statistic, such as the three-
year average of the nth-highest daily maximum 8-hour average O3 
concentration, as an alternative to an expected exceedance statistic. 
Air quality analyses presented in the Staff Paper indicate that, for 
example, the 3-year average of the annual third highest daily maximum 
8-hour concentration provides approximately the same health protection 
as the 3-expected-exceedance form averaged over the same period. 
Similarly, the 3-year average of the annual fifth-highest daily maximum 
8-hour average concentration approximately corresponds to an expected-
exceedance form that allows five expected exceedances averaged over 
three years.
    The CASAC acknowledged that selecting from this range of 
alternative forms is a policy judgment, especially given the nature of 
the health effects and the absence of a ``bright line'' that clearly 
differentiates between acceptable and unacceptable risks within this 
range. However, CASAC did

[[Page 65731]]

recommend that a more robust, concentration-based form (one that would 
allow for multiple exceedances) be adopted to provide additional 
stability in control programs, and thus in public health protection, by 
insulating an area from the impacts of extreme meteorological events 
(Wolff, 1995b).
    In reaching her proposed decision on the form of the standard, the 
Administrator first assessed the degree of health protection that would 
be provided by alternative expected-exceedance forms of the standard. 
Having decided to propose a level of 0.08 ppm for an 8-hour primary 
standard, as discussed above, the Administrator focused on the degree 
of risk reduction that would be achieved by a 1-expected-exceedance 
form as compared to a 5-expected-exceedance form. Examination of the 
quantitative risk assessment results discussed above revealed that, 
within the range of one to five expected exceedances, the dominant 
factor in determining the degree of risk reduction achieved is the 
level of the standard, with the number of expected exceedances being 
associated with smaller differences in risk estimates within a 
continuum of risk.
    In considering possible forms within the range of one to five 
expected exceedances, the Administrator took into account as the 
foremost consideration the adequacy of public health protection 
provided. This includes consideration of (1) aggregate risk for those 
health effects for which quantitative risk analyses have been done; (2) 
consideration of exposures associated with those effects for which no 
quantitative risk estimates could be developed; and (3) the magnitude 
of peak measurements of 8-hour average O3 concentrations, and the 
number of days on which the level of the standard would likely be 
exceeded, based on an analysis of historical air quality data (Freas, 
1996). Based on these considerations, the Administrator judges that the 
middle of the range, three expected exceedances, would represent a 
reasonable policy choice. Relative to a standard set at the upper end 
of the range (i.e., a 5-expected-exceedance standard), a 3-expected-
exceedance standard would serve to better limit the number of days in 
which the level of the standard would be exceeded in areas that just 
attain the standard 9, as well as limiting the magnitude of peak 
measurements of 8-hour average O3 concentrations that would occur 
in such areas.10 A 3-expected-exceedance standard would also 
provide significantly increased stability relative to a standard set at 
the lower end of the range (i.e., the current 1-expected-exceedance 
form 11). The Administrator believes that such a policy choice 
would appropriately reflect the advice of CASAC.
---------------------------------------------------------------------------

    \9\ Areas that ``just attain the standard'' are defined as those 
whose design value falls between 0.075 and 0.084 ppm. Based on 1993-
1995 air quality data, 95% of monitoring sites that just attain a 
0.08 ppm standard with a 3-expected-exceedance form would have 6 or 
fewer days on which the standard would be exceeded, in the worst of 
the three years, as compared to 10 days or fewer days with a 5-
expected-exceedance form (Freas, 1996).
    \10\ Based on 1993-1995 air quality data, 4% of monitoring sites 
that just attain a 0.08 ppm standard with a 3-expected-exceedance 
form would have 8-hour peak O3 concentrations (in terms of the 
4th highest daily maximum concentration in three years) above a 
benchmark level of 0.09 ppm, as compared to 22% of such sites with a 
5-expected exceedance form (Freas, 1996).
    \11\ In comparing alternative 8-hour standards to the current 
standard (0.12 ppm, 1-hour average) with a 1-expected-exceedance 
form, 77% of monitoring sites that just attain the current standard 
would have 8-hour peak O3 concentrations (in terms of the 4th 
highest daily maximum concentration in three years) above a 
benchmark level of 0.09 ppm.
---------------------------------------------------------------------------

    The Administrator also considered whether the form should be 
expressed in terms of expected exceedances or generally equivalent 
concentration-based statistics. As discussed in the Staff Paper, a 
concentration-based statistic has certain advantages over the expected-
exceedance form. The principal advantage is that a concentration-based 
form is more directly related to the ambient O3 concentrations 
that are associated with health effects. That is, given that there is a 
continuum of effects associated with exposures to varying levels of 
O3, the extent to which public health is affected by exposure to 
ambient O3 is related to the actual magnitude of the O3 
concentration, not just whether the concentration is above a specified 
level. With an exceedance-based form, days on which the ambient O3 
concentration is well above the level of the standard are given equal 
weight to those days on which the O3 concentration is just above 
the standard (i.e., each day is counted as 1 exceedance), even though 
the public health impact on the two days is significantly different. 
With a concentration-based form, days on which higher O3 
concentrations occur would weigh proportionally more than days with 
lower O3 concentrations, since the actual concentrations are used 
directly in determining whether the standard is attained. Further, 
based on analyses of historical air quality data (Freas, 1996), 
concentration-based forms control peak measures of O3 
concentrations somewhat better than the corresponding exceedance-based 
forms 12, although exceedance-based forms tend to limit the 
numbers of days on which the level of the standard is exceeded somewhat 
better than concentration-based forms 13. A concentration-based 
form also has greater temporal stability than the expected-exceedance 
form and, thus, would facilitate the development of more stable 
implementation programs by the States.
---------------------------------------------------------------------------

    \12\ For example, whereas 4% of monitoring sites that just 
attain a 0.08 ppm standard with a 3-expected-exceedance form would 
have 8-hour peak O3 concentrations above the benchmark of 0.09 
ppm, only 1% of such sites with a 3rd (or 2nd) highest daily maximum 
concentration form would do so. Similarly, whereas 22% of just-
attain sites with a 5-expected-exceedance form would have peak 
concentrations above the 0.09 ppm benchmark, 17% of such sites with 
a 5th highest daily maximum concentration form would do so.
    \13\ For example, whereas 95% of monitoring sites that just 
attain a 0.08 ppm standard with a 3-expected-exceedance form would 
have 6 or fewer days on which the standard would be exceeded, in the 
worst of the three years, with a 3rd highest concentration form 95% 
of such sites would have 7 or fewer such days. Similarly, with a 5-
expected-exceedance form, 95% of such sites would have 10 or fewer 
such days, as compared to 11 or fewer days with a 5th highest 
concentration forms (Freas, 1996).
---------------------------------------------------------------------------

    Taking the factors discussed above into account, as well as the 
advice of CASAC and the observations and conclusions discussed in the 
Staff Paper, the Administrator believes that the primary standard 
should be expressed in terms of concentrations rather than expected 
exceedances. As indicated above, the 3-year average of the annual 
third-highest daily maximum 8-hour average O3 concentration would 
provide approximately the same degree of health protection as the 3-
expected-exceedance form averaged over the same period. Accordingly, 
the Administrator proposes to express an 8-hour primary standard of 
0.08 ppm as the 3-year average of the annual third-highest maximum 8-
hour average O3 concentration, so as to reduce risk sufficiently 
to protect at-risk populations, including outdoor children, outdoor 
workers, and persons with preexisting respiratory disease, against 
adverse health effects with an adequate margin of safety. Such a 
standard would also provide a more stable basis upon which the States 
can design and implement their O3 control programs. Given the 
range of views discussed in the above section on level of the standard, 
however, the Administrator also solicits comment on other 
concentration-based forms within the range of the second- to the fifth-
highest daily maximum 8-hour average O3 concentrations.

[[Page 65732]]

    The Administrator has also considered whether the above conclusions 
on the form of a standard would be affected if she selected one of the 
alternative levels of a standard discussed in the previous section. 
During the last review of the O3 criteria and standards the CASAC 
concluded that the existing 1-hour standard of 0.12 ppm O3 
provides little, if any, margin of safety, and during this review the 
new evidence focuses on effects below the level of the current NAAQS. 
In general, the risks projected (based on air quality analyses) for a 
3-expected-exceedance form of a 0.09 ppm standard are only marginally 
below those estimated to occur upon attainment of the current NAAQS. 
Taking these factors into account, the Administrator judges that 
consideration of a form for an alternative 0.09 ppm 8-hour standard 
should be limited to the third-highest daily maximum 8-hour average 
O3 concentration, averaged over 3 years, so as not to relax the 
level of protection afforded by the current standard. With regard to 
the alternative of a possible 0.07 ppm 8-hour standard, the 
Administrator judges that the conclusions discussed above with respect 
to the 0.08 ppm level are applicable, such that consideration of the 3-
year average of the annual third-highest daily maximum 8-hour average 
O3 concentration is appropriate, with comment solicited on forms 
within the range of the second to the fifth highest.
    The Administrator recognizes that none of the levels and forms 
under consideration would provide a risk-free standard, due to the 
continuum of risk likely posed by exposures to ambient O3 
potentially down to background levels. Accordingly, the Administrator 
believes, consistent with the advice of CASAC, that it would be 
appropriate to provide additional information to the public about the 
nature of risks associated with exposures to ambient O3. Such 
information could be particularly useful to extremely sensitive 
individuals in making personal decisions about avoiding exposures with 
the potential to cause transient adverse effects on days when 8-hour 
average O3 concentrations are predicted to be at or near the level 
of the proposed standard. As discussed in Section III below, one way to 
provide such information might be in conjunction with the Pollutant 
Standards Index already in use in many metropolitan areas.
    A number of commentors have raised the issue of whether data from 
multiple monitoring sites, rather than data from the highest monitor 
might be used to determine when the primary standards for O3 are 
attained.14 These commentors have suggested that some form of 
averaging across monitors might be appropriate in order to increase the 
degree to which monitoring data used in determining attainment of the 
standard reflects population exposure and aggregate population health 
risk. Averaging data from multiple monitors in an area would produce a 
more stable measure of air quality, and could take into account broader 
population exposure patterns across an area than would the current 
approach of considering data from each monitor independently. When 
considering averaging approaches for O3, it should be recognized 
that the bulk of the human health effects evidence supporting the 
decision on an appropriate O3 standard is based on controlled 
human exposure studies that relate known O3 exposures directly to 
responses in individuals.15 Moreover, as discussed previously in 
this notice, the O3 exposure analysis and the lung function and 
respiratory symptoms components of the health risk assessments, which 
were considered in developing this proposal, reflect the movement of 
people through time and space within an urban area and incorporate air 
quality data from the various monitors within each urban area in 
estimating population exposure and health risk for various population 
groups. For these reasons, it would be considerably more difficult to 
determine an appropriate level for a spatially averaged primary 
standard.
---------------------------------------------------------------------------

    \14\ Spatial averaging of monitoring data is also discussed in 
the notice of a proposed decision on the PM NAAQS published today, 
specifically with regard to an annual PM2.5 standard. Different 
considerations apply in the two cases principally because of 
differences between (1) the nature of the health effects evidence 
for O3 and PM2.5; (2) a single proposed O3 standard, 
in contrast to the proposed suite of annual and 24-hour PM2.5 
standards; and (3) the existence of an established, extensive 
O3 monitoring network, in contrast to the absence at present of 
such a network for PM2.5.
    \15\ In contrast, estimates of excess hospital admissions 
associated with O3 and all of the human health effects evidence 
relating particulate matter to various responses are based on 
relationships between responses in population groups and pollutant 
concentrations observed at ambient fixed site monitors.
---------------------------------------------------------------------------

    In any case, the Administrator does not believe it would be 
appropriate to consider averaging monitors across broad areas [e.g., a 
Consolidated Metropolitan Statistical Area (CMSA) or a Metropolitan 
Statistical Area (MSA)] because such averaging would not be reflective 
of the variability of O3 concentrations across larger metropolitan 
areas. However, it may be appropriate to consider averaging monitors 
across smaller geographic areas within a CMSA/MSA if zones can be 
defined that better reflect the gradient of O3 concentrations and 
associated population exposure. Any approach to averaging across 
monitors within an urban area must take into account not only the 
desirability of providing better characterizations of overall 
population exposure, where possible, but also concerns about whether 
adequate health protection would be provided to individuals within the 
populations that live or work in areas within a CMSA that routinely 
experience higher O3 concentration levels.
    In defining smaller geographic areas within which EPA might permit 
spatially averaged O3 data (hereafter referred to as ``spatial 
averaging zones'), it would be necessary to consider the variability of 
O3 concentrations across the broader metropolitan area as 
reflected in the monitoring data. Ozone air quality concentrations vary 
significantly across most urban areas; the lowest concentrations 
typically occur in the urban center and in locations near O3 
precursor sources, mid-range concentrations in neighborhoods and areas 
surrounding the urban center, and peak concentrations are typically 
measured downwind along the outermost suburban regions of the urban 
area. Also, the location of residences, schools, parks, and other areas 
where individuals might be exposed more frequently to ambient O3 
concentrations of concern should be considered. In order for a 
spatially averaged value to represent potential individual exposures 
within the spatial averaging zone, the O3 pollution concentration 
gradients within each of these spatial averaging zones would need to be 
relatively homogeneous. Otherwise, there may be significant numbers of 
sensitive individuals exposed to high O3 concentrations in areas 
where the spatial average indicates that the overall air quality is 
acceptable.
    Spatial averaging would also have implications for the existing 
O3 monitoring infrastructure. Although a number of larger 
metropolitan areas have extensive O3 monitoring networks, more 
than half of the 234 MSA's with O3 monitoring networks have only 1 
or 2 O3 monitoring sites. If a spatially averaged form of the 
O3 NAAQS were to be adopted, EPA expects that the density of most 
O3 monitoring networks would have to be increased, and/or that 
relocation of some O3 monitoring sites might be necessary.
    To help State and local governments devise different O3 
monitoring networks, the EPA would revise the 40

[[Page 65733]]

CFR Part 58 Ambient Air Quality Surveillance regulation and associated 
guidelines. In so doing, EPA would most likely define general criteria 
for monitoring network design, siting, and spatial averaging zones in 
nationally implementable terms; however, because of the variability of 
the O3 pollution problem across the nation, a locally conducted 
case-by-case evaluation of each O3 monitoring network, and the 
identification of appropriate zones for spatial averaging, would be 
necessary. This activity would place additional burdens on State and 
local air quality management agencies.
    The Administrator believes that before such an averaging approach 
could be given appropriate consideration, the above concerns would need 
to be addressed. Thus, the Administrator solicits comment on whether it 
would be desirable to adopt some form of spatial air quality averaging 
for O3 and on specific alternative approaches that might be 
adopted. In particular, the Administrator is interested in analyses 
that inform questions about monitoring network design, siting 
requirements, and approaches for specification of spatial averaging 
zones; the distribution of public health protection that would result 
from alternative approaches; and the extent to which the level of the 
standard would need to be adjusted, if any, to provide public health 
protection consistent with the level of protection contemplated in this 
proposal.

D. Proposed Decision on the Primary Standard

    After carefully considering the information presented in the 
Criteria Document and the Staff Paper, the advice and recommendations 
of CASAC, and for the reasons discussed above, the Administrator 
proposes to replace the existing 1-hour primary standard with a new 8-
hour, 0.08 ppm primary standard. The new 8-hour standard would become 
effective 30 days after the date of promulgation. To facilitate 
continuity in public health protection during the transition to a new 
standard (see memorandum from John S. Seitz to Mary D. Nichols, 
November 20, 1996; Docket No. A-95-58, item II-B-3), the Administrator 
also proposes except for two limited purposes (attainment 
demonstrations and reclassifications) that the revocation of the 
existing 1-hour standard would become effective at the time EPA 
determines that an area's State implementation plan provides for the 
achievement of the proposed new 8-hour standard. The EPA's plans for 
assuring an effective transition from the existing 1-hour standard to 
the proposed new 8-hour standard are proposed in the Interim 
Implementation Policy notice published elsewhere in today's Federal 
Register.
    The proposed 0.08 ppm, 8-hour primary standard would be met at an 
ambient air quality monitoring site when the 3-year average of the 
annual third-highest daily maximum 8-hour average O3 concentration 
is less than or equal to 0.08 ppm. Data handling conventions are 
specified in proposed revisions to Appendix H, as discussed in Section 
V below.
    The EPA solicits comments on alternative levels of 0.09 ppm, which 
generally represents the continuation of the present level of 
protection, as well as its proposed level of 0.08 ppm, an increased 
level of protection. The EPA also solicits comment on an alternative 8-
hour standard at a level of 0.07 ppm and on retaining the current 
primary standard.

III. Communication of Public Health Information

    Information on the public health implications of ambient 
concentrations of criteria pollutants is currently made available 
primarily through two EPA programs. Under section 303 of the Act, EPA 
identifies exposure levels that constitute ``an imminent and 
substantial endangerment to the health of persons.'' The EPA 
regulations (40 CFR 51.16) require the States to adopt contingency 
plans to prevent ambient pollutant concentrations from reaching these 
significant harm levels (SHLs). The SHL for O3 is that level of 
O3 at which serious and widespread health effects occur among the 
general population. With respect to the existing 1-hour O3 NAAQS 
of 0.12 ppm, the SHL is 0.60 ppm, averaged over 2 hours. In developing 
strategies for implementing the proposed revision of the existing 
NAAQS, EPA will consider corresponding changes in the SHL and propose 
revisions as appropriate in conjunction with other proposed revisions 
to the 40 CFR Part 51.
    Another program, known as the Pollutant Standards Index (PSI) has 
long been in use to provide accurate, timely, and easily understandable 
information about daily levels of pollution (40 CFR 58.50). The PSI 
establishes a uniform system of indexing pollution levels for O3, 
carbon monoxide, nitrogen dioxide, particulate matter and sulfur 
dioxide. Reported PSI values 16 enable the public to know whether 
air pollution levels in a particular location are characterized by EPA 
as good, moderate, unhealthful, or worse. The PSI converts pollutant 
concentrations in a community's air to a number on a scale of 0 to 500. 
On that scale, the number 100 corresponds to the NAAQS for each 
particular pollutant. For the current O3 NAAQS, a 1-hour average 
reading of 0.12 ppm is translated into a PSI value of 100. A PSI value 
in excess of 100 has meant that a pollutant is in the ``unhealthful'' 
(or worse) range on a given day; a PSI value at or below 100 has meant 
that a pollutant reading is in the satisfactory (moderate or good) 
range. Should the current 1-hour O3 NAAQS be replaced by an 8-hour 
NAAQS as proposed, the PSI index would likely be revised to reflect 8-
hour average concentrations.
---------------------------------------------------------------------------

    \16\ PSI values are reported in all metropolitan areas of the 
U.S. with populations 200,000.
---------------------------------------------------------------------------

    In addition, EPA and local officials use the PSI as a public 
information tool to advise the public about the general health effects 
associated with different pollution levels and to describe whatever 
precautionary steps may need to be taken if air pollution levels rise 
into the unhealthful range. By notifying the public when a PSI value 
exceeds 100, citizens are given the opportunity to take appropriate 
steps to avoid exposures of concern. This use of the PSI could be 
expanded to provide more specific health information for O3 
concentrations close to the level of the primary standard. Given the 
continuum of risks associated with exposure to O3, this 
information, while perhaps of interest to all citizens, would be 
particularly useful to those individuals who are extremely sensitive to 
relatively low O3 concentrations. More specifically, the PSI could 
be expanded to include two new descriptive categories in the Index, one 
including concentrations within a range somewhat below the level of the 
new primary standard, the other including concentrations within a range 
somewhat above the level of the standard. Such an approach could better 
reflect the increased understanding of health effects associated with 
O3 exposure developed during this review, and would be consistent 
with the recommendation of a number of CASAC panel members ``that an 
expanded air pollution warning system be initiated so that sensitive 
individuals can take appropriate `exposure avoidance' behavior'' 
(Wolff, 1995b).
    For example, for concentrations somewhat below the level of the 
proposed standard, a new PSI category could be created with a 
descriptor such as ``moderately good.'' This category could be defined 
to correspond to 8-hour O3 levels such as 0.07 to 0.08 ppm. Eight-
hour average O3 concentrations in this range potentially induce 
functional

[[Page 65734]]

and symptomatic responses that are small and mild, respectively, for 
most individuals, but could limit activity for a very small number of 
individuals within the subpopulation of those with impaired respiratory 
systems or who are otherwise extremely sensitive to O3 exposure. 
An expanded warning system thus could include a caution to such 
individuals to consider reducing prolonged moderate to heavy exertion 
outdoors on days with O3 concentrations in this range.
    Further, at concentrations somewhat above the level of the proposed 
standard, for example, a new PSI category could be created with a 
descriptor such as ``moderately unhealthful.'' This category could be 
defined to correspond to 8-hour O3 levels such as 0.09 to 0.10 
ppm. Exposures to 8-hour average O3 concentrations in this range 
are associated with an increase in the number of individuals who could 
potentially experience effects, including moderate or greater 
functional (e.g., 10 to 20% or greater decrements in FEV1) and 
symptomatic (e.g., cough, chest discomfort) responses. An expanded 
warning system thus could include a stronger caution, of interest to 
all citizens and, in particular, to individuals with impaired 
respiratory systems and especially sensitive individuals in the at-risk 
populations of active outdoor children and workers to consider limiting 
prolonged moderate to heavy exertion outdoors on such days.
    For a health advisory system to be effective, citizens need to be 
notified as early as possible to be able to avoid exposures of concern. 
Should the current 1-hour primary NAAQS for O3 be replaced with an 
8-hour standard, there would clearly be increased value in using 
forecasted O3 concentrations in providing cautionary statements to 
the public. When a health advisory indicates that the current 1-hour 
O3 PSI value of 100 has been exceeded, citizens generally have 
time to avoid exposures of concern because O3 levels tend to 
remain elevated for several hours during the day. With an 8-hour 
standard, however, this may not be the case, since by the time a PSI 
value is reported, the potential for prolonged exposures of concern 
would likely have passed for that day. Forecasting 8-hour maximum 
O3 concentrations would facilitate the risk-reduction function of 
the PSI by giving citizens more time to limit or avoid exposures of 
concern.
    Several State and local air pollution control agencies are already 
issuing health advisories based on forecasted O3 concentrations. 
Methodologies currently used for forecasting 1-hour maximum O3 
concentrations include both the use of sophisticated empirical 
meteorological models as well as photochemical models that combine 
emissions inventory data and predicted meteorological conditions. These 
two modeling approaches could be adapted for use in estimating the 
expected 8-hour average maximum O3 concentration value for the 
same or next day.
    By using historical O3 monitoring data and meteorological 
data, empirical meteorological models using various statistical 
regression techniques could be constructed that would provide an 
estimate of the expected same or next day's maximum 8-hour average 
O3 concentration, given current and projected conditions. Input 
model parameters could be defined in the course of the construction of 
such a statistical model, and would involve those parameters providing 
the most predictive capability, such as current and expected mixing 
depth, current and expected boundary layer wind speeds and 
temperatures, and O3 monitoring data for the last several days.
    Alternatively, by using an existing photochemical modeling 
emissions inventory, current and projected meteorological conditions 
could be used to simulate the next day's (or several days') O3 
concentrations. Cities and areas already experiencing high O3 
concentrations would likely have the needed emissions inventory data 
and experience with relevant photochemical models. New capabilities are 
rapidly advancing in providing meso-scale 17 meteorological 
forecasts that might prove useful in augmenting or supporting the 
development of either of these modeling approaches. For instance, the 
National Oceanic Atmospheric Administration is currently refining its 
ability to provide operational meso-scale forecasts of meteorological 
conditions on a 48 kilometer grid that covers all of the United 
States.18
---------------------------------------------------------------------------

    \17\ Meso-scale is a scale larger than the largest thunderstorm 
clusters (3 kilometers) and smaller than roughly 3000 kilometers.
    \18\ See Internet web page, http://nic.fb4.noaa.gov:8000/
research/mesoscale2.html.
---------------------------------------------------------------------------

    Another possible approach to enhance forecasting relates to the 
development of a program to facilitate the sharing of real-time O3 
data among neighboring States. Further, data from O3 air quality 
monitoring networks show that O3 concentrations across large urban 
areas can be highly variable. Thus, issuing geographically-targeted 
forecasts, to reflect these spatial variations in O3 
concentrations, could more appropriately limit the focus of a health 
advisory to locations in which individuals are likely to be at risk. 
Such programmatic enhancements to the PSI could better reflect both a 
change to an 8-hour averaging time and the temporal and spatial 
variations in air quality that occur across urban areas.
    The EPA is not formally proposing to revise the PSI at this time. 
However, the Administrator requests comment on the potential usefulness 
of health effects information of the type discussed above, and the 
appropriateness of using the PSI as a mechanism to convey such 
information to the public, as well as comment on potential new PSI 
categories and associated descriptors, levels, and cautionary 
statements. Comment is also requested on related issues such as the 
practicality of adopting forecasting methods and geographically-
targeted forecasts. The EPA may propose such revisions to the PSI in 
conjunction with future proposals associated with the implementation of 
a revised NAAQS.
IV. Rationale for Proposed Decision on the Secondary Standard
    This notice presents the Administrator's proposed decision to 
replace the existing 1-hour O3 secondary NAAQS with one of two 
alternative new standards: a standard that is identical to the proposed 
0.08 ppm, 8-hour primary standard or, alternatively, a new seasonal 
standard expressed as a sum of hourly concentrations greater than or 
equal to 0.06 ppm, cumulated over 12 hours per day during the maximum 
3-month period during the O3 monitoring season, set at a level of 
25 ppm-hour.
    As noted in the Background section of this notice, this Act defines 
public welfare effects as including but not limited to ``effects on 
soils, water, crops, vegetation, manmade materials, animals, wildlife, 
weather, visibility and climate, as well as effects on economic values 
and on personal comfort and well-being.'' (Emphasis added) The explicit 
inclusion of economic values in the list of potential public welfare 
effects of the presence of criteria pollutants in the ambient air has 
led to the suggestion by some that EPA may consider a broad array of 
economic values, including both the potential disbenefit as well as the 
benefits associated with reducing air pollution in making decisions 
with regard to secondary standards.
    A broad construction of disbenefits might include costs of control. 
EPA's longstanding view of the Clean Air Act is that the statute 
precludes the Agency from considering costs in making such decisions. 
Section 109 directs that any secondary standard specify a level of air

[[Page 65735]]

quality that, ``based on [the air quality] criteria [provided for under 
section 108], is requisite to protect the public welfare from any known 
or anticipated adverse effects associated with the presence of such air 
pollutant in the ambient air.'' Section 108, in turn, states that those 
criteria must ``accurately reflect the latest scientific knowledge 
useful in indicating the kind and extent of all identifiable effects on 
public health or welfare * * *.'' (Emphasis added.) Nothing in this 
language provides any indication that EPA may base its decision on the 
secondary standards on factors other than the effects of the pollutant 
at issue on welfare. This contrasts with other provisions of the Act, 
in which Congress explicitly directed the Administrator to consider 
costs in making her decision (e.g., section 111). Beyond that, the 
parallel structure of section 109's provisions on primary and secondary 
standards, combined with the exclusive emphasis on the effects of the 
pollutant itself in both of those provisions, suggests that Congress 
did not intend a different treatment of cost in relation to setting 
secondary standards from what would apply for primary standards.
    The relevant case law confirms this. In Lead Industries Assn. v. 
EPA, 647 F.2d 1130 (D.C. Cir. 1980), which involved a challenge to 
EPA's failure to consider costs in setting the primary standard for 
lead, the Court rejected industry's claim that EPA must consider costs 
in setting primary standards. The court's rationale applied equally to 
secondary standards. Specifically, the Court held that:

    [T]he statute and its legislative history make clear that 
economic considerations play no part in the promulgation of ambient 
air quality standards under Section 109.

647 F.2d at 1148. (Emphasis added.) The Court later declared:

    Where Congress intended the Administrator to be concerned about 
economic and technological feasibility, it expressly so provided. 
[Citation to Section 111 as an example.] In contrast, Section 109(b) 
speaks only of protecting the public health and welfare.

Id. See also, Natural Resources Defense Council v. Administrator, 902 
F.2d 962 (D.C. Cir. 1990).

    A closely related issue is whether and how EPA may consider, in 
setting secondary standards, any alleged negative effect that reducing 
ambient concentrations of the relevant pollutant or its precursors may 
have on public welfare. For example, it has been suggested that 
reductions of NOx, a precursor of O3, could result in both 
positive and negative benefits. Lower NOx emissions would reduce 
the adverse effects of nitrogen deposition on sensitive aquatic and 
terrestrial systems, but in some localities such reductions could 
result in a possible disbenefit of reduced fertilization of nitrogen 
deficient soils. Notwithstanding EPA's view of the law, or any 
particular finding as to the potential disbenefits outlined above, EPA 
solicits comment on the view that economic values be broadly construed 
to include the possible disbenefits and benefits resulting from 
implementation of standards for the purpose of establishing secondary 
standards.
    The proposal is based on a thorough review of the latest scientific 
information, as assessed in the Criteria Document, on vegetation 
effects associated with exposure to ambient levels of O3. It also 
takes into account and is consistent with: (1) Staff assessments of the 
most policy-relevant information in the Criteria Document and staff 
analyses of air quality, vegetation exposure and risk, and economic 
values presented in the Staff Paper, upon which staff recommendations 
for a new O3 secondary standard are based; (2) consideration of 
the degree of protection to vegetation potentially afforded by the 
proposed new 0.08 ppm, 8-hour primary standard; (3) CASAC advice and 
recommendations as reflected in discussion of drafts of the Criteria 
Document and Staff Paper at public meetings, in separate written 
comments, and in CASAC's letter to the Administrator (Wolff, 1996); and 
(4) public comments received during development of these documents 
either in conjunction with CASAC meetings or separately.
    All CASAC panel members agreed that ``damage is occurring to 
vegetation and natural resources at concentrations below the present 1-
hour national ambient air quality standard (NAAQS) of 0.12 ppm,'' and 
the vegetation experts agreed that ``plants appear to be more sensitive 
to ozone than humans'' (Wolff, 1996). Further, the CASAC panel agreed 
``that a secondary NAAQS, more stringent than the present primary 
standard, was necessary to protect vegetation from ozone,'' although 
``agreement on the level and form of such a standard is still elusive'' 
(Wolff, 1996).
    This review has focused on O3 effects on vegetation, including 
agricultural crops, since these effects are of most concern at O3 
concentrations typically occurring in the United States. By affecting 
crops and native vegetation, O3 may also indirectly affect natural 
ecosystem components such as soils, water, animals, and wildlife, 
although such impacts are not quantifiable at this time. Based on the 
scientific literature assessed in the Criteria Document, the 
Administrator believes it is reasonable to conclude that a secondary 
standard protecting the public welfare categories of crops and 
vegetation from known or anticipated adverse effects would also afford 
increased protection to the other related public welfare categories. 
With regard to O3 effects on manmade materials and deterioration 
of property, the scientific literature assessed in the Criteria 
Document contains little new information since the last review. 
Accordingly, EPA again concludes for the reasons set forth in 1993 (58 
FR 13008, March 9, 1993) that O3 effects on materials do not 
provide a basis for selecting an averaging time and level for a 
secondary standard. In addition, since the effects of O3 on 
personal comfort and well-being (e.g., nose and throat irritation, 
chest discomfort, and cough) have been accounted for in the review of 
the primary standard, these effects are not considered in the review of 
the secondary standard.
    The rationale for proposing to revise the O3 secondary NAAQS, 
presented below, includes consideration of: (1) vegetation effects 
information to inform judgments as to the likelihood that exposures to 
ambient O3 result in adverse public welfare effects, (2) 
information on biologically relevant measures of exposure, (3) insights 
gained from air quality, exposure, risk, and economic benefits 
assessments that provide a broader perspective for judgments about 
protecting public welfare from any known or anticipated adverse 
effects, and (4) specific conclusions with regard to the elements of a 
standard (i.e., averaging time, form, and level) that, taken together, 
would be appropriate to protect public welfare.

A. Effects on Vegetation

    Exposures to O3 have been associated quantitatively and 
qualitatively with a wide range of vegetation effects including: (1) 
visible foliar injury, (2) growth reductions and yield loss in annual 
crops, (3) growth reductions in tree seedlings and mature trees, and 
(4) effects that can have impacts at the forest stand and ecosystem 
level. Since the last review, new information has been published in the 
scientific literature and assessed in the Criteria Document on the 
effects of O3, particularly with respect to forest tree species, 
both seedlings and mature trees, as well as with respect to the 
dynamics of exposure. Discussed below are key findings for each of the 
above

[[Page 65736]]

effects categories drawn from section VII.D of the Staff Paper.
1. Visible Foliar Injury
    Visible foliar injury can be an effect of concern either when it 
directly represents loss of the intended use of the plant, ranging from 
reduced yield and marketability to impairment of the aesthetic value of 
individual plants and natural landscapes, or when it serves as an 
indicator of the presence of concentrations of O3 in the ambient 
air that are associated with more serious effects. Visible foliar 
injury cannot serve as a reliable surrogate measure for other O3-
related vegetation effects because other effects have been reported 
with or without visible injury.
    Both the concentration and the duration of O3 exposures are 
important factors in eliciting visible foliar injury. For example, as 
cited in the Staff Paper, to protect public welfare from visible foliar 
symptoms for crops, O3 concentrations in the range 0.10 to 0.25 
ppm for a duration of 1 hour were identified as a limiting value, which 
decreased to 0.04 ppm to 0.09 ppm when duration of exposure was 
increased to 4 hours. For trees, the ranges of concentrations were 
slightly higher, including 0.06 to 0.17 ppm at the 4-hour duration. 
Flower size was significantly reduced in three species of flowering 
ornamentals when exposed to O3 for 6 hours/day for periods of days 
to weeks, at concentrations from 0.10 to 0.12 ppm, and flower color was 
reduced at the same or lower concentration without visible injury to 
plant leaves. Ozone concentrations of 0.10 ppm for 3.5 hours/day for 5 
days or 0.20 ppm for 2 hours were high enough to elicit injury in most 
turf grasses.
    On a larger scale, foliar injury is occurring on native vegetation 
in natural parks, forests, and wilderness areas, and may be degrading 
the aesthetic quality of the natural landscape, a resource important to 
public welfare. For example, in the east, injury to white pine has been 
observed in the Jefferson and George Washington National Forests and 
throughout the Blue Ridge, including areas of the Shenandoah National 
Park, that experienced an average of five episodes (i.e., any day with 
a 1-hour concentration > 0.08 ppm) during the growing season, with 
episodes lasting from 1 to 3 consecutive days. In the Great Smoky 
Mountains National Park, surveys in the summers of 1987 to 1990 found 
that 95 plant species exhibited foliar injury symptoms consistent with 
O3 damage. During this period, O3 monitoring data indicated 
both elevated concentrations and prolonged exposures to O3, 
especially at the higher elevation sites.
    At western sites, in the Sierra Nevada and Sequoia National 
Forests, appearance of chlorotic mottle of pines increased from 
approximately 20% in 1977 to 55% in the high O3 year of 1988. 
Sequoia National Forest and Sequoia-Kings Canyon National Park 
experience high O3 levels of concern, with mean hourly averages 
ranging from 0.018 to 0.076 ppm, and annual hourly maxima of 0.11 to 
0.17 ppm for 1987. Since 1991, there has been an annual survey of the 
amount of crown injury by O3 to the same trees in approximately 33 
sample plots located in several National Parks and Forests in the 
Sierra Nevada Mountains. Injury symptoms are still being observed in 
ponderosa and Jeffrey pine as well as the less sensitive big cone 
Douglas fir.
2. Growth/Yield Reductions in Annual Crops
    Ozone can interfere with carbon gain (photosynthesis) and 
allocation of carbon with or without the presence of visible foliar 
injury. As a result of decreased carbohydrate availability, remaining 
carbohydrates may be allocated to sites of injured tissue or employed 
in other repair or compensatory processes, thus reducing the 
carbohydrates available for plant growth and/or yield. Growth 
reductions can indicate that plant vigor is being compromised which can 
lead to yield reductions in commercial crops.
    As discussed in the Staff Paper, the National Crop Loss Assessment 
Network (NCLAN) studies undertaken in the early to mid-1980's provide 
the largest, most uniform database on the effects of O3 on 
agricultural crop species. The NCLAN protocol was designed to produce 
crop exposure-response data representative of the areas in the U.S. 
where the crops were typically grown. In total, 15 species accounting 
for greater than 85% of U.S. agricultural acreage planted were studied. 
Of these 15 species, 13 species including 38 different cultivars were 
combined in 54 cases representing unique combinations of cultivars, 
sites, water regimes, and exposure conditions.
    Crops were grown under typical farm conditions and exposed in open-
top chambers to ambient O3 and increased O3 above ambient 
(i.e., modified ambient). The modified ambient treatments contained 
numerous high peaks (hourly O3 concentrations above 0.10 ppm), 
occurring more frequently than in typical ambient air quality 
distributions. Such exposure patterns have raised questions among some 
researchers as to the relative importance of large numbers of high 
O3 peaks versus cumulative mid-level exposures in associations 
between reported effects and various measures of O3 exposures. 
Exposure durations in these studies were species dependent but 
typically went from stand establishment to harvest (an average 28 days) 
and some crops were grown in more than one geographical region and 
repeated over years. In addition, baseline controls were exposed to 
approximately 0.025 ppm O3, which is lower than typical background 
levels in some crop areas. These aspects of the NCLAN protocols 
contribute to the uncertainty inherent in extrapolating controlled 
field study results of percentage yield reductions to non-chambered 
ambient field conditions and crop regions having different O3 air 
quality distributions. Despite these uncertainties, a major advantage 
of the NCLAN approach compared to other study designs is that it allows 
for the use of regression analyses to develop exposure-response 
functions, allowing for prediction of yield loss as a function of 
O3 exposure levels across the range of treatment levels, 
cultivars, and growing conditions used in the studies.
    Based on regression of NCLAN analyses, at least 50% of the species/
cultivars tested exhibited a 10% yield loss (relative to a 0.025 ppm 
baseline concentration) at a 7-hour seasonal mean O3 concentration 
of 0.05 ppm or more. These findings have also been reported in terms of 
various cumulative exposure indices that address better the varying 
patterns of exposure. Using one particular exposure index, the 3-month, 
12-hour SUM06 index 19, 50% of species/cultivars tested were 
predicted to exhibit between 10 and 20% yield loss (relative to a 
baseline SUM06 concentration of 0 ppm-hour) across the range of 25 to 
38 ppm-hour.
---------------------------------------------------------------------------

    \19\ The SUM06 exposure index cumulates over a given time period 
and diurnal window all hourly O3 concentrations greater than or 
equal to 0.06 ppm.
---------------------------------------------------------------------------

    Other studies cited in the Staff Paper examined effects of O3 
on agricultural crops using different methodologies. One methodology 
used ethylene diurea (EDU) as a control to study O3 effects under 
ambient conditions. These studies indicate that yields were reduced by 
18 to 41% relative to the chemically protected controls when ambient 
O3 concentrations exceeded 0.08 ppm during the day for 5-18 days 
over the growing season.
3. Growth Reductions in Tree Seedlings and Mature Trees
    Since preparation of the 1986 Criteria Document, a number of new 
studies

[[Page 65737]]

have been published relating O3 exposure to effects on deciduous 
and evergreen seedlings and mature trees. These studies help to address 
a significant gap in O3 effects data identified by EPA in the last 
review.
    The relationship between the responses of seedlings and those of 
mature trees to O3 exposure is not well understood. Several 
studies cited in the Staff Paper describe a number of differences 
between seedlings and mature trees including stomata number on the 
leaves, photosynthetic rate, water use efficiency, nutritional needs, 
recycling capacities, and canopy effects (e.g., sun vs. shade, wind 
speed, CO2 concentrations) that may explain the varying sensitivities 
of seedling and mature trees to O3 exposures. As a result, data 
from tree seedling studies cannot, at this time, be extrapolated to 
quantify responses to O3 in mature trees.
    A study, cited in the Staff Paper, conducted in Shenandoah National 
Park compared the growth of seedlings and productivity of herbaceous 
vegetation grown in charcoal-filtered air in open-top chambers to that 
in open plots and found that tulip poplar, green ash, sweet gum, black 
locust, several evergreen species (e.g., Eastern hemlock, Table 
mountain pine, pitch pine and Virginia pine), common milkweed, and 
common blackberry all demonstrated growth suppression. Except for the 
last two species, almost no visible injury symptoms accompanied the 
growth reduction.
    The EPA's National Health and Environmental Effects Research 
Laboratory--Western Ecology Division initiated a research program to 
address the effects of O3 on forest tree seedlings. Using the same 
open-top chamber methodology as NCLAN, this program developed exposure-
response functions for six deciduous species, including aspen, red 
alder, black cherry, red maple, sugar maple, and tulip poplar and five 
evergreen species, including douglas fir, ponderosa pine, loblolly 
pine, eastern white pine, and Virginia pine. Similar to crops, these 
studies showed that sensitivity to O3 varied significantly between 
tree type and growth strategy and between species and types within 
species.
    When the distribution of the relative biomass losses for various 
percentiles of the deciduous and evergreen studies are aggregated (see 
Table VII-3 of the Staff Paper), a 12-hour SUM06 exposure of 33.3 ppm-
hours over 92 days is associated with less than 10% biomass reduction 
(relative to a baseline SUM06 concentration of 0 ppm-hour) in 50% of 
the seedling cases studied. When evaluated separately, deciduous 
seedlings exhibited somewhat greater sensitivity than evergreen 
seedlings, on average.
    When compared to the yield reductions in NCLAN studies, the 
seedlings show less biomass loss, on average, than the yield reductions 
exhibited by crops at any given exposure level. Such comparisons (e.g., 
yield loss in annuals vs. biomass loss in perennials) should be viewed 
with caution given the absence of more complete information on other 
aspects of plant response. Moreover, other studies cited in the Staff 
Paper report that very sensitive black cherry seedlings and aspen 
clones experienced 10% biomass loss (relative to a baseline SUM06 
concentration of 0 ppm-hour) when exposed to much lower SUM06 exposures 
regimes (9 to 13 ppm-hour). These data suggest that, given the mean 3-
month SUM06 value at monitored sites over the 10 year period 1982-1991 
of 29.5 ppm-hour (shown in Table VII-1 of the Staff Paper), the 
potential for biomass loss in such sensitive seedling species could be 
significant.
    In assessing the seedling studies, it should be further recognized 
that the influence of multiple environmental factors (e.g., drought, 
nutrient level, site factors, pest/pathogen interactions) were not 
taken into account because the seedlings were grown under optimal 
growing conditions and the genomes studied may not represent the 
complete range of sensitivities within a given species. These factors 
make it problematic when trying to predict effects on perennial species 
growing in an ecosystem context.
    Long-term observational studies of mature trees have also been 
conducted. In both the Cumberland Plateau in Tennessee and San 
Bernardino National Forest, significant reductions in growth in white 
pine individuals and ponderosa pine respectively have been reported. 
While these growth reductions are not attributed to O3 alone, it 
is reported that O3 was a significant contributor that potentially 
exacerbated the effects of other environmental stresses.
    Several other field studies cited in the Staff Paper reported 
growth reduction in mature eastern white pine. A comparison of growth 
rates of mature eastern white pine in the Blue Ridge Mountains of 
Virginia from periods 1955-1959 with those in 1974-1978 indicates 
decreases of 26, 37, and 51% for trees characterized as O3 
tolerant, intermediate, and sensitive, respectively. Because no 
significant change in seasonal precipitation occurred over the same 
time period, the effects on growth were attributed to O3, which 
during the later period reached peaks frequently in excess of 0.12 ppm 
and monthly averages of 0.05--0.07 ppm on a recurring basis. Monitoring 
in the same area revealed peak hourly averages > 0.08 ppm for the 
months April-September in 1979 and 1980. As early as 1979, it was 
concluded by researchers that the most sensitive eastern white pine 
were so severely injured by O3 exposure that they were probably 
being removed from the population.
    Growth rate changes in O3-stressed ponderosa and Jeffrey pine 
have been evaluated in the western United States. Major decreases in 
growth were reported to have occurred for both symptomatic (i.e., 
visible O3 injury) and asymptomatic trees during the 1950's and 
1960's. The percentage of trees exhibiting growth decreases at any 
given site never exceeded 25% in a given decade, and mean annual radial 
increment in trees with visible symptoms of O3 injury was 11% less 
than at sites where trees showed no O3 injury. Larger trees and 
trees older than 100 years showed greater decreases in growth than 
smaller and younger trees.
    The responses of a number of fruit and nut trees to O3 
exposure were also reported in the Staff Paper. Almond has been 
identified as the most sensitive, but peach, apricot, pear, and plums 
have also been affected. Growth reductions were observed in almond, 
peach, and apricot when exposed once weekly for four months to 0.25 
ppm-hour O3 for 4 hours (a high level of exposure generally 
experienced only in fruit and nut tree growing areas in California). 
Other studies examined O3 effects on citrus and avocado. Valencia 
orange trees (during a production year) exposed to a seasonal 12-hour 
mean of 0.04 and 0.075 ppm O3 had 11 and 31% lower yield 
respectively than trees grown in filtered air with a very low O3 
seasonal 12-hour mean concentration of 0.012 ppm. Avocado growth was 
reported to be reduced by 20 or 60% by exposure to 12-hour seasonal 
means of 0.068 and 0.096 ppm O3, respectively, during two growing 
seasons.
4. Forest and Ecosystem Effects
    Plant populations can be affected by O3 exposures, 
particularly when they contain many sensitive individuals. Changes 
within sensitive populations, or stands, if they are severe enough, 
ultimately can change community and ecosystem structure. Structural 
changes that alter the ecosystem functions of energy flow and nutrient 
cycling can arrest or reverse ecosystem development.

[[Page 65738]]

    The San Bernardino forest ecosystem, which has experienced chronic 
O3 exposures over a period of 50 or more years, is the only known 
example of the above sequence of events in which O3 exposures have 
been determined to be a fundamental stressor. From 1968 to 1972, the 
average daily maximum for total oxidants for each month was measured at 
Rim Forest (5,640 ft.), in the San Bernardino Region, where the highest 
concentrations are usually recorded. For the months of May through 
August, the average daily maximum for total oxidants went from a low of 
0.14 ppm in 1969 to approximately 0.28 ppm in 1971, with concentrations 
rarely going below 0.05 ppm at night at this elevation. Ozone 
concentrations exhibited a cyclic diurnal pattern, with the monthly 
average of hourly values ranging from 0.07 to 0.10 ppm at 10:00 am and 
from 0.15 to 0.22 ppm at 4:00 pm. The primary effect of O3 at 
these high levels was that the most susceptible members of the forest 
community, ponderosa and Jeffrey pine, could no longer compete 
effectively for essential nutrients, water, light and space. As a 
consequence, there was a decline in the sensitive species and an 
increase in more tolerant ones.20
---------------------------------------------------------------------------

    \20\ Subsequent to this time period, based on data from 1976 to 
1991, O3 levels in this area have declined from these high 
concentrations.
---------------------------------------------------------------------------

    Beginning with injury to the ponderosa and Jeffrey pine, other 
major changes in the San Bernardino ecosystem were observed in surveys 
during the period 1973 and 1978. Foliar injury, premature senescence, 
and needle fall decreased the photosynthetic capacity of stressed pines 
and reduced the production of carbohydrates resulting in a decrease in 
radial growth and in the height of stressed trees. Numerous other 
organisms and processes were also affected either directly or 
indirectly, including successional patterns of fungal microflora and 
relationship to the decomposer community. Nutrient availability was 
influenced by the heavy litter and thick needle layer under stands with 
the most severe needle injury and defoliation. The composition of 
lichens was significantly reduced.
    For the period 1974 to 1988 there was an improvement shown in the 
injury index used to describe chronic injury to crowns of ponderosa and 
Jeffrey pines attributable to lower O3 levels in the San 
Bernardino region. It was observed, however, that ponderosa and Jeffrey 
pines with slight to severe crown injury lost basal area in relation to 
competing species that are more tolerant to O3. In effect, stand 
development was reversed and the development of the normal fire climax 
mixture dominated by ponderosa and Jeffrey pines was altered.
    Ozone has also been reported to be a selective pressure among 
sensitive tree species (e.g., eastern white pine) in the east. The 
nature of community dynamics in eastern forests is different, however, 
than in the west, consisting of a wider diversity of species and uneven 
aged stands, and the O3 levels are less severe. Therefore, lower 
level chronic O3 stress in the east is more likely to produce 
subtle long-term forest responses such as shifts in species 
composition, rather than wide-spread community degradation. Dieback of 
the spruce-fir forests has occurred in the Appalachian mountains. 
Though these high elevation forests are exposed to a broad range of air 
pollution stresses including O3, the loss of spruce-fir has been 
attributed principally to insect attack. It has not been determined 
whether there is a link between the insect damage cited as the cause of 
the tree death and the role of O3 in predisposing trees to insect 
attack.

B. Biologically Relevant Exposure Indices

    The specification of an exposure index for vegetation must include 
an appropriate averaging time, diurnal window (i.e., the hours during 
the day), and form. Key observations, based on the information 
presented in section VII of the Staff Paper, regarding each aspect of 
an exposure index for vegetation are summarized below.
    An appropriate averaging time to protect against vegetation effects 
of O3 should take into account the cumulative impact of repeated 
peak and mid-level O3 exposures over the entire growing season. 
There is, however, significant variability in growth patterns and 
lengths of growing seasons among the wide range of vegetation species 
that may experience adverse effects associated with O3 exposure. 
Because of this, the selection of any single averaging time for a 
national standard will of necessity be a compromise relative to the 
range of growing seasons for all vegetation species of concern. Based 
on an assessment of the available information in the Staff Paper, the 
Administrator believes that the consecutive 3-month period with maximum 
O3 concentrations in the O3 season is a reasonable surrogate 
for the various periods of plant sensitivity to O3 identified in 
vegetation effects research and most likely covers adequately the 
periods of greatest plant sensitivity.
    The second aspect related to specifying an appropriate exposure 
index is the diurnal window over which O3 concentrations are 
cumulated in computing a seasonal average. While studies assessed in 
the Staff Paper have reported that increasing the diurnal window from 7 
to 12 to 24 hours captures more of the peak and mid-level O3 
concentrations that occur in some environments, the associated 
reductions in growth or yield and increases in foliar injury have not 
been observed to increase proportionally with the increasing diurnal 
period. This observation is consistent with other findings that growth 
and yield reductions are in large part the result of decreases in 
carbohydrate production through photosynthesis, which only occurs in 
daylight hours, and that the majority of plants, although not all, have 
significantly reduced stomatal conductance at night. As a result, the 
Administrator judges that the potential for significant impacts from 
night time O3 exposures is very low.
    Based on the above considerations, the Administrator judges that an 
exposure index that is based on the consecutive 3-months with maximum 
O3 concentrations in the O3 season with a 12-hour diurnal 
window, including the daylight hours from 8:00 am to 8:00 pm, would 
capture biologically relevant exposures for the wide range of 
vegetation growing in environmental conditions found across the United 
States. The Administrator recognizes, however, the differing views 
among the experts on the CASAC panel on these characteristics of an 
appropriate index.
    Specifying the form of a seasonal exposure index intended to 
correspond to the relationship between vegetation response and O3 
exposure is complicated by the many biological variables that influence 
the uptake of O3 by the plant and plant responses to such uptake. 
In spite of the large number of studies that have been conducted to 
evaluate the effects of O3 on vegetation, only a few studies 
assessed in the Staff Paper can be used directly to evaluate the 
differential effects of specific ranges or patterns of O3 
concentrations on plant responses.
    Based on an assessment of these key studies as well as other 
biological effects information reported in the Criteria Document and 
Section VII of the Staff Paper, the Administrator concurs with the 
unanimous view of CASAC that the current standard of 0.12 ppm, 1-hour 
average, does not provide adequate protection, based on the following 
observations: (1) Peak O3 concentrations  0.10 ppm can 
be phytotoxic to a large number of plant species, and can produce acute 
foliar injury responses, reduced crop yield and biomass production, and 
(2) mid-range O3

[[Page 65739]]

concentrations (0.05 to 0.09 ppm) have potential over a longer duration 
of creating chronic stress on vegetation that can result in reduced 
plant growth and yield, shifts in competitive advantages in mixed 
populations, decreased vigor leading to diminished resistance to pest 
and pathogens, and injury from other environmental stresses. Some 
sensitive species can experience foliar injury and growth and yield 
effects even when concentrations never exceed the upper end of the mid-
range concentrations. Because the relative importance of peak 
concentrations and mid-range concentrations in predicting plant 
response depends on numerous factors controlling stomatal conductance 
and other regulators of plant sensitivity, the Administrator believes, 
consistent with CASAC's views, that no one concentration-weighted 
exposure index can be characterized as best accounting for the complex 
relationship between O3 concentrations and plant responses across 
a wide range of species.
    With this limitation in mind, the EPA focused its assessments on 
two particular concentration-weighted indices, the SUM06 and 
W126,21 that have been reported to perform about equally well as 
exposure measures to predict the exposure-response relationships 
observed in the NCLAN crop studies. In the absence of other effects 
studies designed to examine the differences in predictive power between 
these two forms under different exposure regimes and plant growing 
conditions, the Administrator recognizes that the available science 
alone cannot provide an adequate basis for selecting between these 
cumulative concentration-weighted indices. The Administrator, 
therefore, took into account policy considerations in comparing the 
relative advantages of these indices for use in establishing a national 
air quality standard to address seasonal effects of O3 on 
vegetation.
---------------------------------------------------------------------------

    \21\ The W126 exposure index cumulates over a given time period 
and diurnal window all hourly O3 concentrations weighted by a 
specific sigmoidal weighting function.
---------------------------------------------------------------------------

    The W126 exposure index incorporates a weighting function that 
gives increasing value to all concentrations between 0.00 ppm and 0.10 
ppm, with a weight of 1 applied to all concentrations > 0.10 ppm. In 
assessing this form, the Administrator notes that there is insufficient 
scientific information at this time to judge the biological relevance 
of this weighting function, especially at concentrations below 0.05 ppm 
that are within the estimated range of background O3 
concentrations.22 In contrast, the SUM06 form does not include 
O3 concentrations below the cut-point of 0.06 ppm, such that it 
would not be influenced by background concentrations under typical air 
quality distributions.
---------------------------------------------------------------------------

    \22\ At sea level, annual average background values are 
estimated to be between 0.02 and 0.035 ppm O3. Persistent and 
episodic natural sources contribute to background hourly O3 
concentrations in the range of 0.03-0.05 ppm (U.S. EPA, 1996b, p. 
21).
---------------------------------------------------------------------------

    In selecting between these two alternatives, in the absence of 
biological evidence to distinguish between the forms, the 
Administrator, as a matter of policy, judges that a SUM06 index would 
be the more appropriate index for a seasonal secondary standard. In 
reaching this judgment, the Administrator recognizes that there is no 
biological evidence of an effects threshold, and that the effects 
studies we see do not establish that the SUM06 index best accounts for 
all of the biologically relevant exposures. The adoption of a SUM06 
index would, in the Administrator's judgment, provide an appropriate 
complement to the proposed 0.08 ppm, 8-hour primary standard by better 
accounting for the vegetation effects associated with exposures within 
the mid-range concentrations. Because it would not be unduly influenced 
by background concentrations, it would also provide a more appropriate 
target for air quality management programs designed to reduce emissions 
from anthropogenic sources contributing to O3 formation.

C. Vegetation Exposure and Risk Analyses

    In reaching judgments as to the requisite degree of protection 
needed to protect crops and vegetation against the effects of O3, 
the Administrator has taken into account several additional 
considerations, including the extent of exposure of O3-sensitive 
species, potential risks to such species, and monetized and 
nonmonetized benefits associated with reductions in O3 exposures. 
Such considerations help inform judgments as to the degree of 
protection that a secondary NAAQS should provide, and, thus, an 
appropriate level and form for a secondary standard that would provide 
such protection.
    In considering the change in risk to vegetation and potential 
welfare benefits associated with reductions in O3 exposure, the 
Administrator recognizes that significant reductions in O3 
exposures would result from attainment of the proposed primary standard 
discussed above in Section II. Thus, as a matter of policy, she 
believes it is appropriate to evaluate welfare benefits estimated to 
accrue, respectively, from attainment of the 0.08 ppm, 8-hour primary 
standard (as well as alternative 0.09 ppm and 0.07 ppm primary 
standards) as a baseline for the estimation of incremental benefits 
from attainment of alternative seasonal secondary standards.
1. Exposure Characterization
    Though numerous effects of O3 on vegetation have been 
documented as discussed above, it is important in considering risk to 
examine O3 air quality patterns in the U.S. relative to the 
location of O3 sensitive species in order to predict whether or 
not effects are occurring and whether they are likely to occur under 
alternative standards. To address these questions, the EPA assessed the 
available air quality data and conducted national modeling analyses 
since insufficient monitoring data are available for such assessments 
at a national level.
    Because the national air quality surveillance network for O3 
was designed principally to monitor O3 exposure in populated 
areas, there is very limited measured data available to characterize 
O3 air quality in rural and remote sites. For the West, Bohm 
(1992) presents data for the years 1980 through 1988 for all O3 
monitoring sites near Western forests and includes examples of the 
dominant patterns in daily O3 concentrations. Sites located far 
from urban or point source areas experience O3 patterns with 
little hourly variation and few hourly concentrations above 0.06 ppm. 
However, sites on the fringe of urbanized centers or valleys experience 
patterns with some variation in hourly concentrations and typically 
higher O3 concentrations (> 0.10 ppm). In California, for example, 
Yosemite and Sequoia National Parks, which receive pollutants 
transported from highly urbanized areas, had 24-hour means ranging from 
0.036 to 0.085 ppm on 75% of summer days. Lake Gregory, a forested area 
in the western section of the San Bernardino Mountains and situated on 
the eastern fringe of the Los Angeles Basin, California, had diurnal 
means ranging from 0.085 to 0.10 ppm during 49% of summer days. Means 
decreased with altitude and distance from the source. Urban sites have 
fluctuating diurnal patterns, with high afternoon concentrations. 
Marked scavenging of O3 at night contributes to lower diurnal 
means. Outside of California, the patterns are similar, with the 
frequency of occurrence of high O3 levels relating to the size of 
the city and the air pollution potential of the area. The observed 
O3 concentrations

[[Page 65740]]

discussed here are within the ranges associated with vegetation injury.
    In the Eastern United States, studies have been undertaken to 
relate O3 exposure patterns to elevation. As reported in the Staff 
Paper, several sites were monitored in western Virginia from May to 
December 1982 ranging in elevation from 457 m to 1067 m. In general, 
the high elevation site, Big Meadows, in the Shenandoah National Park, 
had higher monthly O3 concentrations than the lower elevation 
sites, yet the number of peak O3 occurrences ( 0.10 
ppm) did not necessarily increase with altitude, suggesting that higher 
monthly averages were associated more with the lack of night time 
scavenging than with a large number of peak hourly concentrations. 
Another study cited in the Staff Paper compared sites for the period 
1988-1992 located in West Virginia, Virginia and Pennsylvania, and 
found the 6 sites with the highest exposures were also the highest 
elevation sites (> 500m). The highest elevation sites were also 
observed to have large numbers of O3 episodes, with a number of 
hourly peaks  0.10 ppm ranging from only a few in 1992 (a 
more typical O3 year) to over 100 in 1988 (a high O3 year). 
In 1988, all 11 sites exceeded the 3-month W126 level (21.0 ppm-hours) 
estimated to result in greater than 10% biomass loss in 50% of the tree 
seedling cases. In other years, except for 1992, more than half the 
sites exceeded this level. While these studies were conducted using a 
W126 exposure indicator rather than the SUM06 form discussed above, EPA 
believes the result would not be substantially different if a SUM06 
indicator had been used. Similar exposure patterns have also been 
reported in the Great Smokies National Park.
    Because of the lack of monitoring data, national air quality 
typical of agricultural crop growing areas has not been characterized. 
Since agricultural sites typically occur at relatively flat, low 
elevation areas, often downwind of large urban areas, they would be 
expected, unlike the high elevation sites discussed above, to 
experience a fluctuating diurnal O3 pattern with O3 levels 
starting low in the early morning and building to a peak in the early 
to late afternoon, before falling to almost background levels at night 
if scavenging agents are present. To characterize exposure patterns 
nationally, EPA conducted analyses using geographic information systems 
(GIS) and data from existing air quality monitoring sites to estimate 
seasonal O3 air quality for the year 1990. The year 1990 was 
selected because it was a typical O3 year (not extremely high or 
low). The estimated seasonal air quality, in terms of the 3-month, 12-
hour, SUM06 exposure index, was used to estimate the potential risk to 
vegetation under 1990 air quality conditions, as well as that predicted 
to occur under alternative standards.
    In taking the results from such analyses into account, the 
Administrator recognizes that there are many sources of uncertainties 
inherent in such analyses. Some of the most important caveats and 
uncertainties concerning the GIS exposure and risk assessments for crop 
yield and biomass loss in seedlings include: (1) Extrapolating from 
exposure-response functions generated in open-top chambers to ambient 
conditions, (2) the lack of a performance evaluation of the national 
air quality extrapolation, (3) the methodology to adjust modeled air 
quality to reflect attainment of various alternative standard options, 
and (4) inherent uncertainties in models to estimate economic values 
associated with attainment of alternative standards. A description of 
the GIS and air quality adjustment methodologies used, as well as the 
associated uncertainties, are discussed in the Staff Paper and related 
technical support documents (Horst and Duff, 1995a,b; Lee and Hogsett, 
1996; Rodecap et al., 1995).
    The regulatory scenarios examined include just attaining the 
existing 1-hour secondary standard, as well as alternative 8-hour 
primary standards, including standards set at 0.08 ppm, with 1- and 5-
expected-exceedance forms, based on a single year of data (1990). These 
estimates of protection provided by the alternative 8-hour, primary 
standards were also used to roughly bound exposure estimates for other 
concentration-based forms under consideration (e.g., the second- and 
fifth-daily maximum 8-hour average O3 concentrations, averaged 
over a 3-year period) by using air quality analyses that compare 
alternative forms of the standard.
    Key observations important in comparing estimated 3-month, 12-hour 
SUM06 exposures under 1990 conditions, with just attaining the existing 
0.12 ppm, 1-hour standard, and the 0.08 ppm, 8-hour alternatives 
include:
    (1) Under 1990 air quality, a large portion of California and a few 
localized areas in North Carolina and Georgia are projected to have 
seasonal O3 levels above those reported to produce greater than 
20% yield loss in 50% of NCLAN crops and 17% biomass loss in seedlings. 
At least a third of the country, again mostly in the Eastern U.S., 
would most likely have seasonal exposures levels which could allow up 
to 10% yield loss in 50% of NCLAN crops and studied seedlings.
    (2) When 1990 air quality is adjusted to simulate attaining the 
current 0.12 ppm, 1-hour secondary standard, the overall seasonal 12-
hour SUM06 exposures improve, but not dramatically. Under this 
attainment scenario, there are still areas of the country judged to 
have seasonal O3 levels sufficient to cause greater than 
(California) or equal to (multistate region in East) 20% and 17% yield 
or biomass loss in crops and trees seedlings, respectively.
    (3) Just attaining the 0.08 ppm, 8-hour, 1- and 5-expected 
exceedance alternatives results in markedly improved air quality when 
compared to just attaining the existing secondary standard, with only 
slight improvements associated with going from a 5- to 1-expected-
exceedance form. The only area projected to exhibit seasonal exposures 
high enough to result in 20% yield loss for crops is a portion of 
southern California, while seasonal exposures in the majority of the 
southeast would be estimated to drop to levels that could allow up to 
10% yield and biomass loss in 50% of NCLAN crops, and studied tree 
seedlings, respectively.
    These results suggest that the proposed 0.08 ppm, 8-hour primary 
standard would provide significantly improved protection of vegetation 
from seasonal O3 exposures of concern. The Administrator 
recognizes, however, that some areas may continue to have elevated 
seasonal exposures, including forested park lands and other natural 
areas, and Class I areas which are federally mandated to preserve 
certain air quality related values.
    To further bound these analyses, EPA also examined 8-hour daily 
maximum and 3-month, 12-hour SUM06 design values for 581 counties 
(those having sufficient monitoring data for the period 1991-1993). As 
discussed in the Staff Paper, this analysis revealed that almost all 
areas that are within or above a SUM06 range of 25-38 ppm-hours would 
also have an 8-hour daily maximum value of greater than 0.08 ppm. Thus, 
in those areas in which air quality monitoring is being conducted, 
areas that would likely be of most concern for effects on vegetation 
would also be addressed by an 8-hour primary standard set at a 0.08 ppm 
level.
    While these analyses indicate that the adoption of an 8-hour, 0.08 
ppm primary standard would provide increased protection, it remains 
uncertain as to the extent to which air

[[Page 65741]]

quality improvements designed to reduce 8-hour O3 concentrations 
would reduce O3 exposures measured by a SUM06 index. The 
Administrator judges this to be an important consideration because: (1) 
The biological database stresses the importance of cumulative, seasonal 
exposures in determining plant response; (2) plants have not been 
specifically tested for the importance of daily maximum 8-hour O3 
concentrations in relation to plant response; and (3) the effects of 
attainment of a 8-hour standard in upwind urban areas on rural air 
quality distributions cannot be characterized with confidence due to 
the lack of monitoring data in rural and remote areas. These factors 
are important considerations in determining whether a separate seasonal 
secondary standard should be adopted.
2. Assessment of Risk to Vegetation
    The EPA has undertaken both quantitative and qualitative 
assessments of O3 risk to vegetation. As discussed in the Staff 
Paper, these assessments predicted that crop loss, under 1990 air 
quality conditions, of greater than 10% (relative to the baseline of 
yield at O3 levels of 0.025 ppm used in the NCLAN studies) would 
occur in some production areas for soybean, kidney bean, wheat, cotton, 
and peanut, with lower yield losses estimated for barley, corn, and 
sorghum. Economic benefits were estimated for the quantifiable effects 
associated with reductions in O3 exposures through attainment of 
alternative standards for agricultural crops as well as California 
fruit and vegetation, as summarized below.
    The persistence of O3 in crop growing regions may also result 
in currently nonquantifiable effects such as reduction in the genetic 
diversity of crop cultivars available, as well as the loss of other 
beneficial traits that may be linked genetically with O3 
sensitivity as a result of breeding programs designed to increase 
yield. Such indirect effects may also occur in plants used in urban 
landscapes and gardens.
    Examination of tree seedlings revealed significant variability in 
projected seedling biomass loss, under 1990 air quality conditions. For 
the most sensitive species studied, black cherry seedling biomass loss 
is projected to be greater than 30% for over half its geographic range. 
The less sensitive white pine and aspen seedlings biomass losses have 
been projected to be up to 10% for 10% of the growing region, but only 
2-3% losses are projected over 50% of their geographic range. Less 
sensitive species studied are projected to have less than 2% seedling 
biomass loss in all areas. Given the uncertainties associated with such 
projections, as discussed in the Staff Paper, these estimates of 
biomass loss represent a potential risk that species may experience at 
least for seedling establishment, reforestation, or natural 
regeneration.
    While it is not possible at this time to scale biomass loss effects 
in seedlings to mature trees, field observations of seedling health and 
mortality can provide information relevant to assessing risk to mature 
trees and forests. Studies cited in the Staff Paper suggest that 
O3 can stress seedlings sufficiently to reduce root growth, thus 
affecting the seedlings' growth, competitiveness, and survivability 
both immediately after germination and in subsequent years.
    The importance of below-ground effects on trees, forests, and 
ecosystems is often overlooked when evaluating responses to O3 
exposure. As discussed in Section VII.B of the Staff Paper, O3 
stress inhibits photosynthesis and reduces the amounts of sugars 
available for transfer to the roots that can alter mycorrhizal 
colonization and compatibility, reducing mycorrhizal formation and root 
growth. Significant reduction and deterioration in feeder roots have 
been observed in O3 damaged white pine and ponderosa pine.
    Beyond biomass loss and impact on root systems, other risks to 
vegetation associated with O3 include shifts in the relationship 
between tree species and insect or pathogens, which can result in 
imbalances within communities that may have long-term effects such as 
those observed in the San Bernardino forests. Ozone effects can also 
reduce biodiversity by selectively impacting particularly sensitive 
O3 species/individuals and by reducing the ability of affected 
areas to provide habitats for other plants or animal species. Moreover, 
O3-sensitive vegetation exists over much of the U.S. including 
National Parks and other Class I areas. The National Park Service has 
reported that sensitive vegetation is being injured by O3 
transported into the parks, affecting not only vegetation of ecological 
importance but also aesthetic and existence values.
3. Economic Benefits Assessment
    As discussed in Section VII.F of the Staff Paper, EPA developed 
estimates of monetized benefits associated with several standard 
alternatives. The analyses focused on commodity crops studied in the 
NCLAN project, representing approximately 75% of the U.S. sales of 
agricultural crops, and California fruits and vegetables that 
constitute approximately 50% of the Nation's fruits and vegetable 
markets. Monetized benefits could not be estimated for other important 
categories such as urban ornamentals, Class I areas, and commercial 
forests because of the lack of concentration response functions and 
appropriate economic valuation models. The available data suggest that 
reductions in ambient O3 levels obtained by the alternative 
standards would confer benefits to these categories as well by reducing 
biomass loss, protecting functional, aesthetic, and existence values, 
and by preserving biodiversity and native habitat.
    Benefits associated with attaining the current NAAQS and a new 8-
hour, 0.08 ppm primary standard, as well as the incremental benefits 
associated with the lowest seasonal secondary standard under 
consideration were estimated. The combined benefits for commodity crops 
and California fruits and vegetables for attaining a new 8-hour, 0.08 
ppm primary standard were reported in terms of a 1-expected-exceedance 
form.23 The key findings from these analyses are:
---------------------------------------------------------------------------

    \23\ As noted in the Staff Paper, there were small differences 
in the forms of the alternative standards analyzed.
---------------------------------------------------------------------------

    (1) Total estimated annual benefits associated with attaining the 
current NAAQS include approximately $160-$340 M in monetized benefits 
from the commodity crops and California fruits and vegetables analyzed, 
as well as some level of benefits from the other benefits categories 
for which no quantitative estimates could be made.
    (2) Total estimated annual benefits associated with attaining a new 
8-hour primary standard of 0.08 ppm, 1-expected-exceedance, include 
approximately $490-$1,420 M in monetized benefits from the commodity 
crops and California fruits and vegetables analyzed, as well as some 
level of benefits from the other benefits categories for which no 
quantitative estimates could be made, although directionally these 
benefits would be expected to be greater than those associated with 
attaining the current NAAQS.
    (3) Incremental annual benefits associated with attaining the 
lowest seasonal secondary standards analyzed include approximately 
$300-$580 M in monetized benefits relative to the current NAAQS, 
compared to approximately $40-$80 M relative to a new 8-hour, 0.08 ppm, 
1-expected-exceedance standard. Additional incremental benefits would 
be obtained for the other benefits categories shown,

[[Page 65742]]

although no quantitative estimates of these additional benefits could 
be made.
    To project monetized benefits nationwide, the above reported 
estimates were scaled upward, by proportionately scaling the monetized 
estimates to the entire market, since the commodity crops included in 
the analyses account for only 75% of the U.S. sales of all agricultural 
crops and the California fruits and vegetables include only 
approximately 50% of the nation's fruit and vegetable markets. The EPA 
recognizes, however, that factors such as the sensitivity to O3 of 
crops and fruits and vegetables not formally analyzed, regional air 
quality, and regional economics introduce considerably uncertainty to 
any such approach to developing a national estimate. Application of the 
scaling approach to the ranges given above results in the following 
rough approximations to national monetized benefits associated with the 
categories of commodity crops and fruits and vegetables:
    (1) National approximation of annual monetized benefits associated 
with attaining the current NAAQS: $270-$530 M.
    (2) National approximation of annual monetized benefits associated 
with attaining a new 8-hour primary standard of 0.08 ppm, 1-expected-
exceedance: $970-$2,270 M.
    (3) National approximation of incremental annual monetized benefits 
associated with attaining the lowest seasonal secondary standards 
analyzed: $490-$910 M relative to the current NAAQS, compared to 
approximately $70-$130 M relative to a new 8-hour, 0.08 ppm, 1-
expected-exceedance standard.
    An examination of the monetized benefits reported above indicates 
that most of the estimated benefits accrue from attainment of the 8-
hour, 0.08 ppm primary standard with a smaller incremental improvement 
obtained by the addition of a seasonal secondary standard. The 
projected national approximations for commodity crops and fruits and 
vegetables suggest that benefits on the order of 1 to more than 2 
billion dollars would result from the proposed 8-hour, 0.08 ppm primary 
standard, alone or in combination with a seasonal secondary standard. 
The EPA also examined the monetized benefits estimates that would 
result from the attainment of either a 0.07 ppm or a 0.09 ppm, 8-hour 
primary standard.24 These estimates suggest that if a 0.07 ppm 8-
hour primary standard were to be attained, only a very small 
incremental improvement in monetized benefits ($40-$80 M) would be 
realized by the addition of the lowest seasonal secondary standard 
analyzed. In contrast, if a 0.09 ppm, 8-hour primary standard were to 
be attained, the incremental benefits to be obtained from the addition 
of the lowest seasonal secondary standard analyzed would be 
considerably more significant ($230-$430 M). The qualitative 
information summarized above also suggests that the monetized benefits 
alone do not fully reflect the public welfare benefits that would be 
obtained from the adoption of the alternative primary standards alone 
or in combination with a new seasonal secondary standard.
---------------------------------------------------------------------------

    \24\ The national approximation of annual monetized benefits 
associated with attaining a 8-hour, 0.07 ppm primary standard alone 
would be $1,120-$3,100 M. This contrasts to $970-$2,270 M for a 0.08 
ppm, 8-hour primary standard alone, and $530-$1,220 M for a 0.09 
ppm, 8-hour primary standard alone.
---------------------------------------------------------------------------

D. Conclusions on Elements of the Secondary Standard

    Based on the assessments of relevant scientific and technical 
information in the Criteria Document, sections VII and VIII of the 
Staff Paper, the views of CASAC, and for the reasons discussed above, 
the Administrator has made the following observations and judgments:
    (1) The existing 1-hour, 0.12 ppm secondary standard does not 
adequately protect vegetation against the adverse effects of O3. 
Peak O3 concentrations >0.10 ppm, but less than the existing 
standard, can be phytotoxic to a large number of plant species, and can 
produce acute foliar injury responses, crop yield loss and reduced 
biomass production. The available scientific information also indicates 
that mid-range concentrations (0.05 to 0.09 ppm) have the potential to 
produce chronic stress on vegetation, resulting in reduced plant growth 
and yield, shifts in competitive advantages in mixed populations, 
decreased vigor leading to diminished resistance to pests, pathogens, 
injury from other environmental stresses, and foliar injury in some 
sensitive species. The quantitative exposure and benefits analysis 
indicate that the risk of such adverse effects would persist even upon 
attainment of the existing standard. The CASAC is unanimously in 
agreement with this conclusion (Wolff, 1996).
    (2) Based on the results of the quantitative exposure and benefits 
analyses, the attainment of the proposed 0.08 ppm, 8-hour primary 
standard would provide substantially improved protection against 
adverse effects of O3 on vegetation. The Administrator recognizes 
that these analyses contain substantial uncertainties, resulting in 
only rough estimates of the benefits associated with alternative 
standards. Nonetheless, the Administrator believes, consistent with 
advice from CASAC (Wolff, 1996), that these analyses can be of use in 
identifying the relative incremental benefits associated with the 
alternative standards. Based on these analyses, a reasonable policy 
choice would be to set the secondary standard identical to the proposed 
0.08 ppm, 8-hour primary standard.
    (3) The Administrator also recognizes, however, that the available 
scientific information on exposure dynamics and their role in producing 
plant response clearly supports the conclusion that a cumulative 
seasonal exposure index is more biologically relevant than a single 
event or mean index. Therefore, for the reasons discussed in section B 
above, the Administrator believes that consideration should also be 
given to establishing a new seasonal secondary standard.
    Having reached these conclusions, the Administrator is proposing 
two alternatives for public comment: (1) Setting the revised secondary 
standard identical to the proposed 0.08 ppm, 8-hour primary standard, 
or (2) establishing a new seasonal secondary standard. These 
alternatives are consistent with the range of views expressed by CASAC 
panel members (Wolff, 1996). The Administrator and CASAC (Wolff, 1996) 
recognize that choosing between these alternatives, as well as 
selecting a specific seasonal exposure index, are policy decisions, and 
that such decisions cannot be based solely on science.
    In specifying the averaging time, form, and level of a new seasonal 
secondary standard, as outlined below, the Administrator has focused 
her consideration on the recommended ranges and key factors outlined in 
the Staff Paper. Such an approach was generally supported by most CASAC 
panel members.
1. Averaging Time
    The Administrator believes that an averaging time for a proposed 
seasonal secondary should be specified as the consecutive 3-month 
period of maximum concentrations in the O3 season with a 12-hour 
diurnal window, including the daylight hours from 8:00 a.m. to 8:00 p.m 
local standard time. In her judgment, such an averaging time will 
adequately address the most biologically relevant periods of exposure 
for both annual and perennial vegetation.

[[Page 65743]]

2. Form
    The Administrator believes that a SUM06 exposure index is a 
reasonable policy choice for a seasonal secondary standard to protect 
against the effects of O3 on vegetation. In reaching this 
determination, the Administrator is particularly mindful that the 
protection provided by the secondary standard should supplement the 
protection provided by the primary standard. A SUM06 form would, in her 
judgement, provide such supplemental protection by cumulating exposure 
over a season reflective of the cumulative nature of O3 effects on 
plants and giving relatively more weight to mid-range exposures of 
concern than to the peak exposures addressed by the proposed 0.08 ppm, 
8-hour primary standard, without being influenced by estimated 
background concentrations that are beyond the scope of control intended 
by a NAAQS.
3. Level
    The level at which a seasonal secondary standard should be set 
depends on policy judgments by the Administrator as to the level of air 
quality the attainment and maintenance of which is requisite to protect 
the public welfare from any known or anticipated adverse effects 
associated with the pollutant in the ambient air. As discussed above 
and in Section VII of the Staff Paper, the EPA undertook a series of 
analyses to examine the incremental improvements in terms of modelled 
exposure potential, monitored air quality, and quantifiable economic 
and other benefits that would accrue from a seasonal secondary 
standard. These analyses indicate that, beyond those achieved by 0.08 
ppm, 8-hour, 1- to 5-expected-exceedance primary standard alternatives, 
relatively smaller incremental improvements would result from the 
adoption of a SUM06 seasonal standard within the range of levels under 
consideration, 38-25 ppm-hour.25 Again, the Administrator 
acknowledges the significant uncertainties in the analyses and 
recognizes that these benefits should be regarded as rough 
approximations.
---------------------------------------------------------------------------

    \25\ Roughly corresponding to the 20 percent and 10 percent 
yield loss protection levels for 50 percent of the NCLAN crops, 
respectively.
---------------------------------------------------------------------------

    Based on these observations, it is the Administrator's judgment, 
taking into account the protection provided by both primary and 
secondary standards, that in the selection of the level for a seasonal 
secondary standard the focus should be on the lower end of the SUM06 
(38-25 ppm-hours) range where a greater degree of incremental 
protection would more likely be expected. Although it was judged that 
this degree of incremental protection may be relatively small at the 
national level, such incremental improvement could be potentially 
significant at regional and local levels where it would be expected to 
provide additional protection for the most sensitive commercial crops 
and tree species, while directionally providing increased protection 
against the more subtle impacts of O3 on vegetation and ecosystem 
resources in Class I and other regions. Thus, the Administrator decided 
to propose a level of 25 ppm-hour for a SUM06 secondary standard.

E. Proposed Decision on the Secondary Standard

    As discussed more fully above, the Administrator took into account 
several factors in reaching her proposed decision on the secondary 
standard. First, she concluded based on information presented in the 
Criteria Document and Staff Paper and discussed above, that the 
existing secondary standard does not provide adequate protection for 
vegetation against the effects of O3. Having reached this 
conclusion, the Administrator next considered: (1) The degree of 
protection afforded by the proposed 8-hour, 0.08 ppm primary standard; 
(2) the incremental protection associated with a SUM06, 25 ppm-hour 
secondary standard; and (3) the value of establishing a seasonal form 
for the secondary standard that is more representative of biologically 
relevant exposures. In weighing these factors, the Administrator 
recognized, as did CASAC, that reaching a decision on revising the 
secondary standard requires a blend of scientific and policy 
considerations.
    Based on the quantitative analyses discussed above and presented in 
detail in Section VII of the Staff Paper, a reasonable policy choice 
could be to set the revised secondary standard identical to the 
proposed 8-hour, 0.08 ppm primary standard. Attainment of such a 
secondary standard would, in the Administrator's judgment, provide 
substantial protection against the effects of O3 on vegetation. 
The Administrator also recognizes, however, that a SUM06 seasonal 
secondary standard would have a stronger scientific basis in that it 
would better account for cumulative, seasonal exposure. The 
Administrator also notes the growing body of evidence, assessed in the 
Criteria Document and Staff Paper, that suggests more subtle impacts of 
O3 acting in synergy with other natural and man-made stressors on 
individual plants, populations and whole systems. While both the Staff 
Paper and CASAC concluded that there is insufficient information as yet 
to estimate the severity of these impacts quantitatively, the 
Administrator is concerned that the available information be given 
proper weight in considering the extent to which a secondary standard 
should be precautionary as to such effects. Given the potential 
significance of the effects, particularly at the regional scale and in 
Class I areas, coupled with the views of many in the scientific 
community that a SUM06 seasonal standard would be more representative 
of biologically relevant exposures, the Administrator believes it is 
important to air these issues fully. Therefore, the Administrator is 
proposing two alternatives for public comment: (1) Setting the revised 
secondary standard identical to the proposed 0.08 ppm, 8-hour primary 
standard in all respects; or (2) establishing a 3 month, 12-hour, SUM06 
seasonal secondary standard, set at the level of 25 ppm-hour.
    As discussed previously, the Administrator has also requested 
comment on two alternative levels for the 8-hour primary standard. 
Accordingly, she has examined the implications for her decision on the 
secondary standard of adopting either of the alternative levels for the 
primary standard. Based on the economic benefits assessment and other 
factors discussed above, adoption of a secondary standard identical to 
a 0.09 ppm, 8-hour standard would provide appreciably less protection 
against vegetation effects than would an 0.08 ppm, 8-hour secondary 
standard. For that reason, the Administrator would be more inclined to 
set a 25 ppm-hour SUM06 seasonal secondary standard if a 0.09 ppm, 8-
hour primary standard were to be selected. On the other hand, if a 0.07 
ppm, 8-hour primary standard were to be selected, appreciably more 
benefits would result as compared to those associated with attainment 
of the proposed 0.08 ppm, 8-hour primary standard. In such a case, the 
Administrator would most likely establish a secondary standard 
identical to a 0.07 ppm, 8-hour primary standard. The EPA solicits 
comments on the implications that the possible selection of one of the 
alternative 8-hour primary standards (i.e., 0.09 or 0.07 ppm) would 
have on the selection of an appropriate secondary standard.
    The Administrator also recognizes the importance of enhancing the 
existing O3 monitoring network to provide better coverage in rural 
areas of agricultural or ecological importance irrespective of the 
final alternative chosen. Because expanding the O3 monitoring 
network

[[Page 65744]]

would impose additional cost burdens, EPA specifically requests public 
comment on the appropriate spatial scale for an enhanced monitoring 
network intended to provide adequate air quality surveillance in more 
rural areas in a cost-effective manner. Such comments will serve to 
inform EPA's development of revised air quality surveillance 
requirements (40 CFR Part 58) that will be proposed at a later date.
    With respect to the proposed seasonal secondary standard, EPA is 
also seeking comment on whether O3 concentrations from several 
monitors should be spatially integrated when determining compliance 
with the standard. Such an approach could provide a more representative 
indication of vegetation exposures over a given area than O3 
concentrations measured at a single monitor. To help inform 
consideration of this approach, EPA specifically requests comment on 
the spatial scale that should be considered for such integration (e.g., 
averaging) and the number of monitors that would be needed to determine 
representative vegetation exposures for a given spatial scale.

V. Revisions to Appendix H--Interpretation of the NAAQS for Ozone

    The EPA is proposing to revise Appendix H to 40 CFR part 50 to 
reflect the proposed revisions to the primary and secondary standards 
discussed above. The proposed revisions to Appendix H would explain the 
computations necessary for determining when the proposed primary and 
secondary standards are met. More specifically, the proposed revisions 
address data completeness requirements, data reporting, handling, and 
rounding conventions, and example calculations. Because two alternative 
secondary standards are proposed, the proposed changes to Appendix H 
address both alternatives: (1) A secondary standard set identical to 
the proposed 0.08 ppm, 8-hour primary standard; or (2) a seasonal 
secondary standard expressed in the SUM06 form. Depending on the final 
decision on the secondary standard, the proposed revisions to Appendix 
H will be modified accordingly.
    Key elements of the proposed revisions to Appendix H are outlined 
below.

A. Data Completeness

    One key change to Appendix H is that the data completeness 
requirements for the proposed 0.08 ppm, 8-hour primary standard (and 
the secondary standard if it is set identical to the primary standard) 
would not include an adjustment to the concentration statistic to 
account for missing data. Instead, the proposal would require 90% data 
completeness, on average, during the 3-year period, with no single year 
within the period having less than 75% data completeness. This data 
completeness requirement would have to be satisfied in order to 
determine that the standard(s) have been met at a monitoring site. A 
site could be found not to have met the standard(s) with less than 
complete data.
    Based on its analysis of available air quality data, the EPA 
believes that the proposed data completeness requirement is reasonable 
given that 90% of all monitoring sites that are operated on a 
continuous basis routinely meet this objective. The EPA is seeking 
comment, however, on whether meteorological data would provide an 
objective basis for determining, on a day for which there is missing 
data, that the meteorological conditions were not conducive to high 
O3 concentrations, and therefore, that the day could be assumed to 
have an O3 concentration less than 0.08 ppm. The EPA specifically 
requests comment on the appropriateness of permitting adjustments for 
missing data based on meteorological conditions, as well as on 
information that would permit better definition of those necessary 
conditions likely to result in peak 8-hour O3 concentrations in 
the ranges of concern.
    For a secondary standard expressed in a 3-month, 12-hour, SUM06 
form, a site would be required to have 75% data completeness in a given 
year and adjustments would be made for missing data. Because this 
alternative is a seasonal cumulative index, representing a distribution 
of O3 values under a range of meteorological conditions, rather 
than a peak statistic, the EPA is proposing a missing data procedure 
that would multiply the unadjusted SUM06 value by the ratio of the 
number of possible daylight hours (8:00 am to 8:00 pm) during the 
O3 monitoring season to the number of hours with valid ambient 
hourly concentrations.

B. Data Handling and Rounding Conventions

    Almost all State agencies now report hourly O3 concentrations 
to three decimal places, in ppm, since the typical incremental 
sensitivity of currently used O3 monitors is 0.001 ppm. In 
calculating 8-hour average O3 concentrations from such hourly 
data, and in calculating 3-year averages of the third highest maximum 
8-hour average concentrations, the calculated fourth decimal place 
digit would be rounded (with 0.0005 rounded up) to preserve the number 
of significant digits in the reported data.
    To determine whether the proposed standard is met, the calculated 
value of the third highest maximum 8-hour average concentrations, 
averaged over three years, would be compared to the level of the 
standard. The proposed standard of 0.08 ppm is expressed to the second 
decimal place, reflective of the quantitative uncertainties in the 
health effects evidence upon which the proposed standard is based. More 
specifically, these uncertainties include the measurement uncertainty 
inherent in the reported ambient O3 concentrations used in field 
and epidemiological studies and in the exposure estimates upon which 
quantitative risk assessments have been based. The EPA believes that 
expressing the proposed standard to the second decimal place is 
consistent with the quality assurance guidelines that indicate the 
precision 26 for such O3 measurements shall be within 
15%.
---------------------------------------------------------------------------

    \26\ The term precision is used to denote both the 
reproducibility of a measurement under a constant set of conditions, 
as well as other components of measurement uncertainty such as 
instrument drift and relative bias.
---------------------------------------------------------------------------

    To compare the calculated 3-year average O3 concentration to 
the level of the standard, the third decimal place of the calculated 
value is rounded. The current rounding convention is to round up digits 
equal to or greater than 5. Rounding has the effects of reducing the 
probability of misclassifying an attainment area as nonattainment and 
of producing a more stable attainment test. Taking into account 
measurement uncertainty and the desirability of these resulting 
effects, EPA has historically deemed the current rounding convention to 
be appropriate.
    On the other hand, EPA recognizes that this current rounding 
convention directionally results in less public health protection than 
that which would be associated with a convention that defined the 
smallest increment of 0.001 ppm to be above the level of the standard 
for the purposes of determining whether the standard has been 
met.27 Thus, EPA solicits comment on the use of an alternative 
rounding convention defined as low as 0.001 ppm, with regard to 
potential increased public health protection as well as to potential 
effects on the probability of

[[Page 65745]]

attainment misclassifications and on the stability of the standard.
---------------------------------------------------------------------------

    \27\ Based on 1993-1995 air quality data, approximately 13 
million more people would live in areas for which the alternative 
rounding convention would result in improvements in air quality as 
compared to the current rounding convention. This population 
difference corresponds to an increase of 66 counties that would not 
meet the proposed primary standard based on the alternative rounding 
convention.
---------------------------------------------------------------------------

VI. Technical Changes to Appendices D and E

A. Appendix D to Part 50--Measurement Principle and Calibration 
Procedure for the Measurement of O3 in the Atmosphere

    Minor revisions to the references listed within Appendix D are 
proposed to provide the reader with the most recent information on 
obtaining reference materials to support the O3 monitoring 
methodology. Specifically, these changes include updating the EPA 
addresses and adding EPA document reference numbers.
    Appendix D also contains information on the ``Temporary Alternative 
Calibration Procedure--(Boric Acid-Potassium Iodide)'' for the O3 
federal reference method. This alternative calibration procedure was 
considered to be a valid alternative to the ultraviolet photometry 
procedure for direct calibration of O3 analyzers for a period 
between the promulgation of the original O3 federal reference 
method and 18 months after promulgation (from February 1979 through 
August 1980). Since this period has expired, it is no longer necessary 
to include the alternative calibration procedure in Appendix D; 
therefore, EPA proposes to remove it.

B. Appendix E to Part 50--Reference Method for Determination of 
Hydrocarbons Corrected for Methane

    Appendix E specifies a reference method that was used when EPA 
established a total hydrocarbon National Ambient Air Quality Standard. 
The total hydrocarbon NAAQS was revoked on January 5, 1983 (48 FR 628), 
and the inclusion of a total hydrocarbon reference method within 
Appendix E is no longer appropriate. Accordingly, the EPA proposes to 
remove it.
    Several sources of information on the current techniques used for 
the measurement of hydrocarbons are available. Two that are widely used 
are the ``Compendium of Methods for the Determination of Toxic Organic 
Compounds in Ambient Air, Method TO-12, Method for the Determination of 
Non-Methane Organic Compounds (NMOC) in Ambient Air Using Cryogenic 
Preconcentration and Direct Flame Ionization Detection (PDFID),'' EPA-
600/4-89-017, National Exposure Research Laboratory, U.S. EPA; and 
``Photochemical Assessment Monitoring Stations Implementation Manual,'' 
Appendix N, EPA-454/B-93-051, March 1994, available through the 
National Technical Information Services (NTIS publication number PB 94 
187 382), 5825 Port Royal Road, Springfield, VA 22161.

VII. Implementation Program

    Recognizing that adoption of new NAAQS for O3, together with 
new particulate matter (PM) NAAQS, as well as potential new regulations 
for regional haze, could have profound implications for existing State 
implementation programs, EPA established a subcommittee under the Clean 
Air Act Advisory Committee (CAAAC) in 1995. The Subcommittee, comprised 
of some 58 members representing environmental organizations, State and 
local air pollution control agencies, Federal agencies, academia, 
industry, and other public interests, is to provide advice and 
recommendations to EPA on developing new, integrated approaches for 
implementing the potential new NAAQS for O3 and PM, as well as a 
potential new regional haze reduction program. The Subcommittee, 
through several work groups made up of Subcommittee members and other 
designees recommended by the Subcommittee, is in the process of 
examining key aspects of the existing implementation programs for 
O3 and PM, to provide for more effective implementation of the 
potential new NAAQS, as well as to provide new approaches to better 
integrate broad regional and national control strategies with more 
localized efforts.
    Upon completion of its work, the Subcommittee will present its 
findings and recommendations to the CAAAC. These recommendations will 
then assist EPA's development of appropriate policies and regulations 
for implementing the potential new O3 and PM NAAQS and regional 
haze regulations in the most efficient and environmentally effective 
manner. These policies and regulations will then be published in the 
Federal Register for further input from the public.

VIII. Regulatory Impacts

    The EPA has judged this proposal to be a significant action, and 
has prepared a draft Regulatory Impact Analysis (RIA) for it as 
discussed below. Neither the draft RIA nor the associated contractor 
reports have been considered in issuing this proposal. Judicial 
decisions make clear that the economic and technological feasibility of 
attaining ambient standards are not to be considered in setting them, 
although such factors may be considered to a degree in the development 
of State plans to implement the standards.
    As discussed above, EPA has established a Subcommittee of the CAAAC 
to examine the existing implementation programs for O3 and PM, and 
provide advice and recommendations to assist EPA in developing new, 
integrated approaches for implementing potential new or revised NAAQS 
for O3 and PM, as well as a potential new regional haze reduction 
program. Because the work of the Subcommittee is still in progress, the 
draft RIA and associated regulatory flexibility assessment that 
accompany this notice do not reflect its advice and recommendations or 
any resulting implementation strategies for O3. The EPA 
anticipates that such strategies will be more efficient and 
environmentally effective than the ones analyzed. While the draft RIA 
and flexibility assessment should be useful in generally informing the 
public about potential costs and benefits associated with 
implementation of the proposed revisions, they do not reflect any new 
implementation or monitoring requirements or policies that may be 
proposed after consideration of the Subcommittee's advice and 
recommendations. As EPA develops and elaborates such requirements or 
policies, it will continue to consult with the Subcommittee and will 
prepare further regulatory analyses as appropriate.

A. Executive Order 12866

    Under Executive Order 12866, the Agency must determine whether a 
regulatory action is ``significant'' and, therefore, subject to Office 
of Management and Budget (OMB) review and other requirements of the 
Executive Order. The order defines ``significant regulatory action'' as 
one that may:
    (1) Have an annual effect on the economy of $100 million or more or 
adversely affect in a material way the economy, a sector of the 
economy, productivity, competition, jobs, the environment, public 
health or safety, or State, local, or tribal governments or 
communities;
    (2) Create a serious inconsistency or otherwise interfere with an 
action taken or planned by another Agency;
    (3) Materially alter the budgetary impact of entitlements, grants, 
user fees, or loan programs or the rights and obligations or recipients 
thereof; or
    (4) Raise novel legal or policy issues arising out of legal 
mandates, the President's priorities, or the principles set forth in 
the Executive Order.
    In view of its important policy implications, this proposal has 
been judged to be a ``significant regulatory action'' within the 
meaning of the Executive Order, and EPA has

[[Page 65746]]

submitted it to OMB for review. Changes made in response to OMB 
suggestions or recommendations will be documented in the public docket 
and made available for public inspection at EPA's Air and Radiation 
Docket Information Center (Docket No. A-95-58).
    The EPA has prepared and entered into the docket a draft regulatory 
impact analysis (RIA) entitled ``Regulatory Impact Analysis for 
Proposed Ozone National Ambient Air Quality Standard (November 1996)''. 
This draft RIA assesses the costs, economic impacts, and benefits 
associated with the implementation of the current and several 
alternative NAAQS for ozone. As discussed in the draft RIA, there are 
an unusually large number of limitations and uncertainties associated 
with the analyses and resulting cost impacts and benefit estimates. 
Because judicial decisions make clear that cost can not be considered 
in setting NAAQS, the results of the draft RIA have not been considered 
in developing this proposal.

  Comparison of Benefits and Costs--Regional Control Strategy Baseline  
                           (Billions of 1990$)                          
          [Estimates are incremental from the current standard]         
------------------------------------------------------------------------
                                                   Monetized            
                                                    annual      Annual  
             Alternative ozone NAAQS               benefits    costs of 
                                                  of partial    partial 
                                                  attainment  attainment
------------------------------------------------------------------------
80 ppb, 8 hour, 4 AX............................      $0-0.6        $0.6
80 ppm, 8 hour, 1 AX............................     0.1-1.5         2.5
------------------------------------------------------------------------

    As discussed in the RIA itself, there are a large number of 
limitations and uncertainties inherent in estimating these national 
costs and benefits over extended periods of time. Results are limited 
by the inability to monetize certain health or welfare benefits for 
comparison with projections of control costs that are usually more 
complete, but are sometimes overstated due to an inability to forecast 
advances in pollution prevention and control. The approaches used for 
the RIA did not attempt to take advantage of flexibilities and savings 
possible in consideration of combined air quality management program 
for the PM and O3. Further, they were limited by availability of 
emissions, air quality monitoring, and related information. Indeed, the 
suite of control measures available to be considered in the cost 
analysis was not sufficient to achieve full attainment in 2007. It is 
for this reason we have only presented the costs and benefits for this 
``partial attainment'' scenario. In the partial attainment scenario, 
there would be 8 to 20 residual nonattainment areas representing 14 to 
32 million people, respectively, in 2007. These areas would need 
approximately 120,000 to 750,000 additional tons of emission reductions 
in order to attain the standards. One implication of this scenario is 
that more time will be needed to attain the standards in the areas 
remaining in nonattainment. Moreover, based on past experience, 
improvements in technologies and creative implementation programs are 
likely to result in more effective programs than can now be forecasted. 
The EPA is planning to improve and expand its analysis of the 
integrated costs and benefits of attaining both the PM and ozone 
standards in association with developing implementation guidance.

B. Regulatory Flexibility Analysis

    The Regulatory Flexibility Act (RFA), 5 U.S.C. 601 et seq., 
provides that, whenever an agency is required to publish a general 
notice of rulemaking for a proposed rule, the agency must prepare 
regulatory flexibility analyses for the proposed and final rule unless 
the head of the agency certifies that it will not have a significant 
economic impact on a substantial number of small entities. In judging 
what kinds of economic impacts are relevant for this determination, it 
is appropriate to consider the purposes and requirements of the RFA. 
Mid-Tex Electrical Co-op v. FERC, 773 F.2d 327, 341-42 (D.C. Cir. 
1985).
    Review of the findings and purposes section of the RFA makes clear 
that Congress enacted the RFA to address the economic impact of rules 
on small entities subject to the rule's requirements. Pub. L. 96-354, 
section 2 (1980); see also 126 Cong. Rec. 21,452, 21,453 (1980). In 
explaining the need for the RFA, Congress generally expressed concern 
about the problematic consequences of applying regulations uniformly to 
large and small entities. Specifically, Congress stated that ``laws and 
regulations designed for application to large scale entities have been 
applied uniformly to small [entities] even though the problems that 
gave rise to government action may not have been caused by those small 
entities, that ``uniform Federal regulatory and reporting requirements 
have in numerous instances imposed unnecessary and disproportionately 
burdensome demands * * * upon small [entities] with limited 
resources,'' that ``the failure to recognize differences in the scale 
and resources of regulated entities has in numerous instances adversely 
affected competition in the marketplace,'' and that ``the practice of 
treating all regulated [entities] as equivalent may lead to inefficient 
use of regulatory agency resources.'' Id. To address these concerns, 
Congress enacted the RFA ``to establish as a principle of regulatory 
issuance that agencies shall endeavor, consistent with the objectives 
of the rule and of applicable statutes, to fit regulatory and 
informational requirements to the scale of the [entity] subject to 
regulation'' (emphasis added). Id.
    The statutory requirements for regulatory flexibility analyses 
confirm that the economic impact to be analyzed is the impact of the 
rule on small entities that will have to comply with the rule's 
requirements. In both initial and final regulatory flexibility 
analyses, for example, the agency issuing the rule is required to 
describe and (where feasible) estimate the number of small entities 
``to which the proposed rule will apply''; describe the reporting, 
recordkeeping and other ``compliance requirements'' of the proposed 
rule; and estimate the classes of small entities that ``will be subject 
to the requirement.'' See RFA sections 603 and 604. The agency must 
also discuss and address significant regulatory alternatives that are 
consistent with the applicable statutes and would minimize any 
significant economic impact on small entities. Among the possible 
alternatives listed by the RFA are the establishment of differing 
compliance and reporting requirements that take into account the 
resources available to small entities and partial or total exemptions 
from the rule for small entities. See RFA section 603(c). The RFA's 
requirements for regulatory flexibility analyses thus establish that 
the focus of such analyses are the regulatory requirements small 
entities will be required to meet as a result of the rule and ways to 
tailor those requirements to reduce the burden on small entities. Mid-
Tex Electrical Co-op, 773 F.2d at 342 (``[I]t is clear that Congress 
envisioned that the relevant ``economic impact'' was the impact of 
compliance with the proposed rule on regulated small entities').
    The scope of regulatory flexibility analyses in turn informs the 
scope of the analysis necessary to support a certification that a rule 
will not have ``a significant economic impact on a substantial number 
of small entities.'' Thus, ``an agency may properly certify that no 
regulatory flexibility analysis is necessary when it determines that 
the rule will not have a significant economic impact on a substantial 
number of small entities that are subject

[[Page 65747]]

to the requirements of the rule.'' Id. (emphasis added); see also 
United Distribution Companies v. FERC, 88 F.3d 1105, 1170 (D.C. Cir. 
1996).
    In view of the RFA's purposes and the requirements it establishes 
for regulatory flexibility analyses, EPA believes that today's proposal 
to revise the O3 NAAQS will not have a significant economic impact 
on small entities within the meaning of the RFA. The proposed rule, if 
promulgated, will not establish requirements applicable to small 
entities. Instead, it will establish a standard of air quality that 
other Act provisions will call on states (or in case of state default, 
the federal government) to achieve by adopting implementation plans 
containing specific control measures for that purpose. In other words, 
state (or federal) regulations implementing the NAAQS might establish 
requirements applicable to small entities, but the NAAQS itself would 
not.28 For these reasons, the Administrator certifies that this 
proposed rule will not have a significant economic impact on a 
substantial number of small entities.
---------------------------------------------------------------------------

    \28\ Because the proposed rule would not establish requirements 
applicable to small entities, EPA can not in fact perform the 
analyses contemplated by the RFA.
---------------------------------------------------------------------------

    While the statutory requirements for regulatory flexibility 
analyses are thus inapplicable to NAAQS standard-setting, EPA is 
nonetheless interested in assessing to the extent possible the 
potential impact on small entities of implementing a revised O3 
NAAQS. EPA has accordingly conducted a more general analysis of the 
potential cost impacts on small entities of control measures that 
states might adopt to attain and maintain a revised NAAQS, and has 
included that analysis in the RIA cited above.
    That analysis examines industry-wide cost and economic impacts for 
those sectors likely to be affected when the proposed revisions to the 
O3 NAAQS are implemented by States. As part of the draft RIA, the 
EPA has analyzed various industries for the existence of small entities 
to ascertain whether small entities within a given industry category 
are likely to be differentially affected when compared to the industry 
category as a whole. This information will serve to inform potentially 
affected small entities, thus enabling them to participate more 
effectively in EPA's review and potential revision of existing 
implementation requirements and policies and in development of any 
necessary State implementation plan revisions. As indicated previously, 
EPA will prepare further analyses as appropriate as it develops new 
implementation requirements or policies.
    The EPA's finding that today's proposal will not have a significant 
economic impact on small entities also entails that the new small-
entity provisions in Section 244 of the Small Business Regulatory 
Enforcement Fairness Act (SBREFA) do not apply. Nevertheless, EPA 
intends to fulfill the spirit of SBREFA on a voluntary basis. To 
accomplish this, following the proposal of new air quality standards 
for ozone and particulate matter, EPA intends to work with the Small 
Business Administration (SBA) to hold two separate panel exercises to 
collect comments, advice and recommendations from representatives of 
small businesses, small governments, and other small organizations. The 
first panel, soliciting comments on the new standards themselves, will 
be held shortly after proposal. The second panel, covering 
implementation of the standards, will be held a few months later. Both 
panel exercises will be carried out using a panel process modeled on 
the ``Small Business Advocacy Review Panel'' provisions in Section 244 
of SBREFA. We are also adding a number of small-entity representatives 
to our Federal advisory committee focusing on NAAQS implementation; we 
expect the small-entity advice from this committee will help the 
aforementioned implementation panel accomplish its purpose.

C. Impact on Reporting Requirements

    There are no reporting requirements directly associated with an 
ambient air quality standard proposed under section 109 of the Act (42 
U.S.C. 7400). There are, however, reporting requirements associated 
with related sections of the Act, particularly sections 107, 110, 160, 
and 317 (42 U.S.C. 7407, 7410, 7460, and 7617). If EPA proposes 
revisions to the air quality surveillance requirements (40 CFR part 58) 
for O3, the associated RIA will address the Paperwork Reduction 
Act requirements through an Information Collection Request.

D. Unfunded Mandates Reform Act

    Title II of the Unfunded Mandates Reform Act of 1995 (UMRA), Pub. 
L. 104-4, establishes requirements for Federal agencies to assess the 
effects of their regulatory actions on State, local, and tribal 
governments and the private sector. Under section 202 of the UMRA, EPA 
generally must prepare a written statement, including a cost-benefit 
analysis, for proposed and final rules with ``Federal mandates'' that 
may result in expenditures to State, local, and tribal governments, in 
the aggregate, or to the private sector, of $100 million or more in any 
one year. This requirement does not apply if EPA is prohibited by law 
from considering section 202 estimates and analyses in adopting the 
rule in question. Before promulgating an EPA rule for which a written 
statement is needed, section 205 of the UMRA generally requires EPA to 
identify and consider a reasonable number of regulatory alternatives 
and adopt the least costly, most cost-effective, or least burdensome 
alternative that achieves the objectives of the rule. These 
requirements do not apply when they are inconsistent with applicable 
law. Moreover, section 205 allows EPA to adopt an alternative other 
than the least costly, most cost-effective, or least burdensome 
alternative if the Administrator publishes with the final rule an 
explanation of why that alternative was not adopted. Before EPA 
establishes any regulatory requirements that may significantly or 
uniquely affect small governments, including tribal governments, it 
must have developed under section 203 of the UMRA a small government 
agency plan. The plan must provide for notifying potentially affected 
small governments, enabling officials of affected small governments to 
have meaningful and timely input in the development of EPA regulatory 
proposals with significant Federal intergovernmental mandates, and 
informing, educating, and advising small governments on compliance with 
the regulatory requirements.
    As indicated previously, EPA cannot consider in setting a NAAQS the 
economic or technological feasibility of attaining ambient air quality 
standards, although such factors may be considered to a degree in the 
development of State plans to implement the standards. Accordingly, EPA 
has determined that the provisions of sections 202, 203, and 205 of the 
UMRA do not apply to this proposed decision. The EPA acknowledges, 
however, that any corresponding revisions to associated State 
implementation plan requirements and air quality surveillance 
requirements, 40 CFR part 51 and 40 CFR part 58, respectively, might 
result in such effects. Accordingly, EPA will address unfunded mandates 
as appropriate when it proposes any revisions to 40 CFR parts 51 and 
58.

E. Environmental Justice

    Executive Order 12848 requires that each Federal agency make 
achieving environmental justice part of its mission by identifying and 
addressing, as

[[Page 65748]]

appropriate, disproportionately high and adverse human health or 
environmental effects of its programs, policies, and activities on 
minorities and low-income populations. These requirements have been 
addressed to the extent practicable in the draft RIA cited above.

List of Subjects in 40 CFR Part 50

    Environmental protection, Air pollution control, Carbon monoxide, 
Lead, Nitrogen dioxide, Ozone, Particulate matter, Sulfur oxides.

    Dated: November 27, 1996.
Carol M. Browner,
Administrator.

References

    American Thoracic Society. (1985) Guidelines as to what 
constitutes an adverse respiratory health effect, with special 
reference to epidemiologic studies of air pollution. Am. Rev. 
Respir. Dis. 131: 666-668.
    Bohm, M. (1992) Air quality and deposition. In: Olson, R.K.; 
Binkley, D.; Bohm, M., eds. The responses of western forests to air 
pollution. New York, NY: Springer Verlag; pp. 63-152 (Ecological 
studies no. 97).
    Horst, R. and M. Duff (1995) Concentration Data Transformation 
and the Quadratic Rollback Methodology (Round 2, Revised). 
Unpublished memorandum to R. Rodriguez, U.S. EPA, June 8.
    Johnson, T. (1994) Letter Report: Enhancements to the PNEM 
summer camp methodology. Prepared by IT/Air Quality Services for 
U.S. EPA, OAQPS; Research Triangle Park, NC, March 21. (For copies, 
contact Harvey M. Richmond, U.S. Environmental Protection Agency, 
OAQPS, MD-15, Research Triangle Park, N.C. 27711, (919) 541-5271.)
    Johnson, T; Capel, J.; Mozier, J.; McCoy, M. (1996a) Estimation 
of ozone exposures experienced by outdoor children in nine urban 
areas using a probabilistic version of NEM. Prepared by IT/Air 
Quality Services for U.S. EPA, OAQPS; Research Triangle Park, NC, 
August.
    Johnson, T.; Capel, J.; McCoy, M.; Mozier, J. (1996b) Estimation 
of ozone exposures experienced by outdoor workers in nine urban 
areas using a probabilistic version of NEM. Prepared by IT/Air 
Quality Services for U.S. EPA, OAQPS; Research Triangle Park, NC, 
August.
    Lee, E.H.; Hogsett, W.E. Methodology for Calculating Inputs for 
Ozone Secondary Standard Benefits Analysis: Part II. Internal 
Memorandum prepared for Eric Ginsburg and Rosalina Rodriguez, OAQPS, 
EPA. March 18, 1996.
    McClellan, R. O., (1989) Letter from Chairman of Clean Air 
Scientific Advisory Committee to the EPA Administrator, dated May 1, 
1989. EPA-SAB-CASAC-LTR-89-019.
    Rodecap, K.; Lee, H.; Herstrom, A.; and Broich, S. Methodology 
for Calculating Inputs for Ozone Secondary Standard Benefits 
Analysis. Internal memorandum to Bill Hogsett, U.S. EPA, NHEERL-WED. 
June 29, 1995.
    Thurston, G.D.; Ito, K.; Kinney, P.L.; Lippmann, M. (1992) A 
multi-year study of air pollution and respiratory hospital 
admissions in three New York State metropolitan areas: results for 
1988 and 1989 summers. J. Exposure Anal. Environ. Epidemiol. 2:429-
450.
    U.S. Environmental Protection Agency (1994) Measuring Air 
Quality: The Pollutant Standards Index. Research Triangle Park, NC: 
Office of Air Quality Planning and Standards; EPA report no. EPA/
451/k-94-001.
    U.S. Environmental Protection Agency (1996a) Air quality 
criteria for Ozone and related photochemical oxidants. Research 
Triangle Park, NC: Office of Health and Environmental Assessment, 
Environmental Criteria and Assessment Office; EPA report nos. EPA/
600/AP-93/004a-c.
    U.S. Environmental Protection Agency (1996b) Review of the 
national ambient air quality standards for ozone: assessment of 
scientific and technical information. OAQPS staff paper. Research 
Triangle Park, NC: Office of Air Quality Planning and Standards; EPA 
report no. EPA-452/R-96-007. Available from: NTIS, Springfield, VA; 
PB96-xxxxxx.
    U.S. Environmental Protection Agency. Technical Assistance 
Document for the Calibration of Ambient Ozone Monitors, EPA 
publication number EPA-600/4-79-057, EPA, National Exposure Research 
Laboratory, Department E, (MD-77B), Research Triangle Park, NC 
27711.
    U.S. Environmental Protection Agency. Transfer Standards for 
Calibration of Ambient Air Monitoring Analyzers for Ozone, EPA 
publication number EPA-600/4-79-056, EPA, National Exposure Research 
Laboratory, Department E, (MD-77B), Research Triangle Park, NC 
27711.
    Whitfield, R.G.; Biller, W.F.; Jusko, M.J.; Keisler, J.M. (1996) 
A probabilistic assessment of health risks associated with short-
term exposure to tropospheric ozone. Report prepared for U.S. EPA, 
OAQPS. Argonne National Laboratory; Argonne, IL, August. (For 
copies, contact Harvey M. Richmond, U.S. Environmental Protection 
Agency, OAQPS, MD-15, Research Triangle Park, N.C. 27711, (919) 541-
5271.)
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Scientific Advisory Committee to the EPA Administrator, dated 
November 28, 1995. EPA-SAB-CASAC-LTR-96-001.
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Scientific Advisory Committee to the EPA Administrator, dated 
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4, 1996. EPA-SAB-CASAC-LTR-96-006.

    For the reasons set forth in the preamble, chapter I of title 40 of 
the Code of Federal Regulations is proposed to be amended as follows:

PART 50--NATIONAL PRIMARY AND SECONDARY AMBIENT AIR QUALITY 
STANDARDS

    1. The authority citation for part 50 continues to read as follows:

    Authority: Secs. 109 and 301(a), Clean Air Act, as amended (42 
U.S.C. 7409, 7601(a)).

    2. Section 50.9 is revised to read as follows:


Sec. 50.9  National primary and secondary ambient air quality standards 
for O3.

    (a) The level of the national primary ambient air quality standard 
for O3, measured by a reference method based on Appendix D to this 
part and designated in accordance with part 53 of this chapter, is 0.08 
parts per million (ppm), daily maximum 8-hour average.
    (b) An 8-hour average shall be considered valid if at least 75% of 
the hourly averages for the 8-hour period are available. In the event 
that only six (or seven) hourly averages are available, the 8-hour 
average shall be computed on the basis of the hours available, using 
six (or seven) as the divisor. The 8-hour averages shall be stated in 
parts per million to three decimal places.
    (c) The primary O3 ambient air quality standard is met at an 
ambient air quality monitoring site when the 3-year average of the 
annual third-highest daily maximum 8-hour average O3 concentration 
is less than or equal to 0.08 ppm. The primary standard is not met when 
the 3-year average of the annual third-highest daily maximum 8-hour 
average O3 concentration is greater than 0.08 ppm. Computations 
for comparisons with the primary standard and data handling conventions 
are specified in Appendix H to this part.
    (d) The national secondary ambient air quality standard for O3 
is based on a 3-month cumulative index that sums all ambient hourly 
concentrations greater than or equal to 0.06 ppm during the hours 8:00 
am to 8:00 pm local standard time (LST). The secondary O3 standard 
is met at an ambient air quality monitoring site when the cumulative 
index value (SUM06) based on a consecutive 3-month period of maximum 
concentrations is less than or equal to 25 ppm-hours. Computations for 
comparisons with the level of the secondary standard and data handling 
conventions are specified in Appendix H to this part.
    3. Appendix D is amended as follows:
    a. References 8 and 9 are revised.
    b. After Figure 2, Schematic Diagram of a Typical UV Photometric 
Calibration System (Option 1), all remaining text included within the 
``Temporary Alternative Calibration Procedure--

[[Page 65749]]

(Boric Acid-Potassium Iodide)'' section is removed.
    c. Figure 1, Schematic Diagram of a Typical BAKI Calibration 
System, Figure 2, KI Sampling Train, and Figure 3, Schematic Diagram of 
a Typical BAKI Calibration System (Option 1), are removed.

Appendix D to Part 50--Measurement Principle and Calibration Procedure 
for the Measurement of O3 in the Atmosphere

* * * * *

References

* * * * *
    8. Transfer Standards for Calibration of Ambient Air Monitoring 
Analyzers for O3, EPA publication number EPA-600/4-79-056, EPA, 
National Exposure Research Laboratory, Department E, (MD-77B), 
Research Triangle Park, NC 27711.
    9. Technical Assistance Document for the Calibration of Ambient 
Ozone Monitors, EPA publication number EPA-600/4-79-057, EPA, 
National Exposure Research Laboratory, Department E, (MD-77B), 
Research Triangle Park, NC 27711.
* * * * *

Appendix E [Removed and Reserved]

    4. Appendix E is removed and reserved.
    5. Appendix H is revised in its entirety to read as follows:

Appendix H to Part 50--Interpretation of the Primary and Secondary 
National Ambient Air Quality Standards for O3

1. General

    This appendix explains the data handling conventions and 
computations necessary for determining whether the national primary 
and secondary ambient air quality standards for O3 specified in 
part 50.9 of this chapter are met at an ambient O3 air quality 
monitoring site. Ozone is measured in the ambient air by a reference 
method based on appendix D of this part. Data reporting, data 
handling, and computation procedures to be used in making 
comparisons between reported O3 concentrations and the level of 
the O3 standard are specified in the following sections.

2. Primary Ambient Air Quality Standard for O3

2.1  Data Reporting and Handling Conventions

    a. Computing 8-hour averages. Hourly average concentrations 
shall be reported in parts per million (ppm) to the third decimal 
place, with additional digits to the right being truncated. Running 
8-hour averages shall be computed from the hourly O3 
concentration data for each hour of the year and the result shall be 
stored in the first, or start, hour of the 8-hour period. An 8-hour 
average shall be considered valid if at least 75% of the hourly 
averages for the 8-hour period are available. In the event that only 
six (or seven) hourly averages are available, the 8-hour average 
shall be computed on the basis of the hours available using six (or 
seven) as the divisor. The 8-hour average O3 concentrations 
shall be rounded to three decimal places (with 0.0005 rounded up) to 
preserve the number of significant digits in the reported data. The 
insignificant digits are truncated.
    b. Daily maximum 8-hour average concentrations. There are 24 
possible running 8-hour average O3 concentrations for each 
calendar day during the O3 monitoring season. (Ozone monitoring 
seasons vary by geographic location as designated in part 58, 
Appendix D to this chapter.) The daily maximum 8-hour concentration 
for a given calendar day is the highest of the 24 possible 8-hour 
average concentrations computed for that day. This process is 
repeated, yielding a daily maximum 8-hour average O3 
concentration for each calendar day with ambient O3 monitoring 
data. Because the 8-hour averages are recorded in the start hour, 
the daily maximum 8-hour concentrations from two consecutive days 
may have some hourly concentrations in common. Generally, 
overlapping daily maximum 8-hour averages are not likely, except in 
those non-urban monitoring locations with less pronounced diurnal 
variation in hourly concentrations.
    c. An O3 monitoring day shall be counted as a valid day if 
valid 8-hour averages are available for at least 75% of possible 
hours in the day (i.e., at least 18 of the 24 averages). In the 
event that less than 75% of the 8-hour averages are available, a day 
shall also be counted as a valid day if the daily maximum 8-hour 
average concentration for that day is greater than the level of the 
ambient standard.

2.2  Primary Standard-Related Summary Statistic

    The standard-related summary statistic is the annual third-
highest daily maximum 8-hour O3 concentration, expressed in 
parts per million, averaged over three years. The 3-year average 
shall be computed using the three most recent, consecutive calendar 
years of monitoring data meeting the data completeness requirements 
described in this appendix. The computed 3-year average of the 
annual third-highest daily maximum 8-hour average O3 
concentrations shall be rounded to three decimal places (with 0.0005 
rounded up) to preserve the number of significant digits in the 
reported data. The insignificant digits are truncated.

2.3  Comparisons With the Primary O3 Standard

    a. The primary O3 ambient air quality standard is met at an 
ambient air quality monitoring site when the 3-year average of the 
annual third-highest daily maximum 8-hour average O3 
concentration is less than or equal to 0.08 ppm. The primary 
standard is not met at an ambient air quality monitoring site when 
the 3-year average of the annual third-highest daily maximum 8-hour 
average O3 concentration is greater than 0.08 ppm. Thus, the 3-
year average annual third-highest daily maximum 8-hour average 
O3 concentration is also the design value for the site. The 
number of significant figures in the level of the standard dictates 
the rounding convention for comparing the computed 3-year average 
annual third-highest daily maximum 8-hour average O3 
concentration with the standard. The third decimal place of the 
computed value is rounded, with values equal to, or greater than 5 
rounding up. Thus, a computed 3-year average O3 concentration 
of 0.085 ppm is the smallest value that is greater than 0.08 ppm.
    b. This comparison shall be based on three consecutive, complete 
calendar years of air quality monitoring data. This requirement is 
met for the three year period at a monitoring site if daily maximum 
8-hour average concentrations are available for at least 90%, on 
average, of the days during the designated O3 monitoring 
season, with a minimum data completeness in any one year of at least 
75% of the designated sampling days.
    c. Although three complete years of data are required to 
demonstrate attainment of the standard, years with high 
concentrations shall not be ignored on the ground that they have 
less than complete data. Thus, in computing the 3-year average 
third-highest maximum concentration, calendar years with less than 
75% data completeness shall be included in the computation if the 
annual third-highest maximum 8-hour concentration is greater than 
the level of the standard.

                      Example 1.--Ambient Monitoring Site Attaining the Primary O3 Standard                     
----------------------------------------------------------------------------------------------------------------
                                                 1st highest  2nd highest  3rd highest  4th highest  5th highest
                                      Percent    daily max 8- daily max 8- daily max 8- daily max 8- daily max 8-
               Year                  valid days   hour conc.   hour conc.   hour conc.   hour conc.   hour conc.
                                                    (ppm)        (ppm)        (ppm)        (ppm)        (ppm)   
----------------------------------------------------------------------------------------------------------------
1993..............................          100        0.092        0.090        0.085        0.083        0.080
1994..............................           96        0.084        0.083        0.075        0.074        0.074
1995..............................           98        0.080        0.079        0.073        0.068        0.065
    Average.......................           98                                  0.078                          
----------------------------------------------------------------------------------------------------------------


[[Page 65750]]

    The primary standard is met at this monitoring site because the 
3-year average of the annual third-highest daily maximum 8-hour 
average O3 concentrations (i.e., 0.078 ppm) is less than or 
equal to 0.08 ppm. The data completeness requirement is also met 
because the average percent of days with valid monitoring is greater 
than 90%, and no single year has less than 75% data completeness.

                   Example 2.--Ambient Monitoring Site Failing To Meet the Primary O3 Standard                  
----------------------------------------------------------------------------------------------------------------
                                                 1st highest  2nd highest  3rd highest  4th highest  5th highest
                                      Percent    daily max 8- daily max 8- daily max 8- daily max 8- daily max 8-
               Year                  valid days   hour conc.   hour conc.   hour conc.   hour conc.   hour conc.
                                                    (ppm)        (ppm)        (ppm)        (ppm)        (ppm)   
----------------------------------------------------------------------------------------------------------------
1993..............................           96        0.105        0.103        0.103        0.102        0.102
1994..............................           74        0.104        0.103        0.092        0.091        0.088
1995..............................           98        0.103        0.101        0.101        0.097        0.095
                                   -----------------------------------------------------------------------------
    Average.......................           89                                  0.099                          
----------------------------------------------------------------------------------------------------------------

    The primary standard is not met at this monitoring site because 
the 3-year average of the third-highest daily maximum 8-hour average 
O3 concentrations (i.e., 0.099 ppm) is greater than 0.08 ppm. 
Note that the O3 concentration data for 1994 is used in these 
computations, even though the data capture is less than 75%, because 
the third-highest daily maximum 8-hour average concentration for 
that year is greater than 0.08 ppm.

3. Secondary Ambient Air Quality Standard for O3

3.1  Data Reporting and Handling Conventions

    a. Computing the daily index value (D.I.). The secondary O3 
standard is based on a seasonal index that accumulates all hourly 
O3 concentrations greater than or equal to 0.060 ppm for each 
hour of the day between 8:00 a.m. to 8:00 p.m. local standard time 
(LST). The reporting requirements are the same as described above 
for the primary standard. The hourly average ambient O3 
concentrations shall be reported in parts per million (ppm) to three 
decimal places, with additional digits to the right being truncated. 
The first step, computing the daily index value, D.I., for the 
daylight hours is illustrated below:

     Example 3.--Sample Daily Index Calculation for an Ambient Ozone    
                             Monitoring Site                            
------------------------------------------------------------------------
   Start hour       Concentration       Start hour       Concentration  
     (a.m.)             (ppm)             (p.m.)             (ppm)      
------------------------------------------------------------------------
12.............           0.034                 12             0.079    
1..............           0.027                  1             0.082    
2..............           0.016                  2             0.085    
3..............           0.014                  3             0.088    
4..............           0.010                  4             0.083    
5..............           0.009                  5             0.081    
6..............           0.014                  6             0.065    
7..............           0.025                  7             0.056    
8..............           0.045                  8             0.051    
9..............           0.060                  9             0.038    
10.............           0.075                 10             0.039    
11.............           0.080                 11            0.034     
------------------------------------------------------------------------
Daily index (D.I.) = 0.060 + 0.075 + 0.080 + 0.079 + 0.082 + 0.085 +    
  0.088 + 0.083 + 0.081 + 0.065 = 0.78 ppm-hours                        

    b. Computing the monthly cumulative index (SUM06). The daily 
index is computed at each monitoring site for each calendar day in 
each month during the O3 monitoring season designated in part 
58, Appendix D to this chapter. At an individual monitoring site, a 
month is counted as a valid O3 monitoring month if ambient 
O3 concentrations are available for at least 75% of possible 
index hours in the month. For months with greater than 75% data 
completeness, the monthly total index value shall be adjusted for 
incomplete sampling by multiplying the unadjusted SUM06 cumulative 
index value by the ratio of the number of possible daylight hours to 
the number of hours with valid ambient hourly concentrations.
    Example 4. Adjusting the monthly SUM06 for missing data.
    [GRAPHIC] [TIFF OMITTED] TP13DE96.000
    
where,

M.I. = the monthly sum of the daylight hours greater than or equal 
to 0.060 ppm,
D.I. = the daily sum of the daylight hours greater than or equal to 
0.060 ppm,
n = the number of days in the calendar month,
v = the number of daylight hours (8:00 a.m.--8:00 p.m. LST) with 
valid hourly O3 concentrations.

3.2  Secondary Standard-related Summary Statistic

    The standard-related summary statistic is the annual maximum 3-
month SUM06 value expressed in ppm-hours. Specifically, the annual 
SUM06 value is computed on a calendar year basis using the three 
highest, consecutive monthly SUM06 values.

3.3  Comparisons with the Secondary O3 Standard

    The secondary O3 standard is met when the annual maximum 
SUM06 value based on a consecutive 3-month period at an O3 air 
quality monitoring site is less than or equal to 25 ppm-hours. 
Values of 0.5 or greater shall be rounded up.

                       Example 5.--Sample Calculation of the Maximum 3-Month SUM06 Value at an Ambient Air Quality Monitoring Site                      
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                  April         May          June         July        August     September     October  
--------------------------------------------------------------------------------------------------------------------------------------------------------
Monthly SUM06................................................        4.442        9.124       12.983       16.153       13.555        4.364        1.302
    3-Month Total............................................           na           na       26.549       38.260       42.691       34.072       19.221
--------------------------------------------------------------------------------------------------------------------------------------------------------

    The maximum consecutive 3-month SUM06 value for this site is 43 
ppm-hours. Because 43 is greater than 25, the secondary O3 
ambient air quality is not met at this ambient air quality 
monitoring site.

[FR Doc. 96-30903 Filed 12-12-96; 8:45 am]
BILLING CODE 6560-50-P